Puebla, Jalisco and Colima. Though the latter two localities are on the present Pacific slope, the fauna is entirely Atlantic in its relationship. In Puebla, these Cretaceous corals belong for the most part to reef-forming genera. So abundant are the remains that during life they must have built reefs of large extent. Throughout the remaining Cretaceous no coral reefs and but few corals are known. The total absence of Pacific Cretaceous fauna in southern Mexico precludes any statement as to the Cretaceous corals of the Pacific Ocean. Atlantic Eocene is known in southern Mexico but no corals have been reported from it. It is probable, however, that they occur, as Eocene coral reefs of some importance are known in the West Indies. On the Pacific side, the Eocene is not known. During the Oligocene reef-building corals reached a degree of abundance along the shores of eastern Mexico never before nor since equalled. In the Tampico Embayment there are, in the San Rafael formation, extensive beds composed almost exclusively of corals. These beds are so characteristic and of such wide extent that they are valuable for correlation purposes. On the Pacific shore the Oligocene is also absent. On the Isthmus of Tehuantepec there are rather extensive exposures of Upper Miocene and Pliocene with Caribbean fauna. In these a few corals of the solitary type occur but no reef-builders are known. No Miocene or Pliocene is known on the west coast of southern Mexico. Curiously enough, near the head of the Gulf of Lower California there is a Miocene or Pliocene reef. The corals of this reef all belong to living genera of the Caribbean Sea. Pleistocene corals occur in lately uplifted beds in the vicinity of Tampico. No reefs, however, have been reported. Along the Oaxaca coast the Pleistocene occurs as a low cliff of loosely consolidated beach material. It extends along the coast in patches for some twenty-eight miles. In some places it is on the beach and in others it is inland about a mile and a half. Its elevation varies from low tide level to fifty feet or more. No reefs have been found in this exposure although there are abundant coral remains which include such reef-forming genera as Porites and Pocillopora. Recent corals occur both along the Atlantic and Pacific coasts of Mexico. With the exception of a few genera that are nearly world wide in distribution, the coral faunas of the two coasts are quite distinct, indicating, I might add in passing, a somewhat lengthy separation. Curiously enough, corals are much more common along the western coast than along the shores of the Gulf of Mexico. It is possible that the explanation of this phenomenon is the same as that of the general paucity of corals along the west coast as compared with the islands of the Gulf of Mexico and Florida waters in general. It appears that this explanation is based on ecological factors that are under coast control. Corals are sessile animals and hence require stability to the base to which they are attached. This condition is best found along rocky shores where the beach sand is limited in amount or does not exist. Sandy beaches and sandy bottoms are particularly unfavorable to either crawling or burrowing or sessile forms. Long stretches of beach sand with only an occasional beach worn shell bear ample witness of this fact. Here the soft shifting sands afford not only no foothold but subject any organism that does not swim to periodic burial which if sufficiently prolonged, is fatal and, what is equally destructive to a coral that cannot close itself up, to actual choking by the sand grains entering into the vital parts. Practically the entire eastern coast of Mexico is a low lying plain that is but a few feet above sea-level. Long sandy beaches and bars extend from Vera Cruz almost continuously to the Rio Grande. Rocky coasts are absent. It is true that there are several areas of elevation but only the soft Tertiary rocks are exposed and they are nearly as hostile to shore life as the sandy beaches. On the west coast, however, a different geological history has been followed by different shore conditions, hence different ecological conditions obtain. Elevated areas alternate with depressed areas. The former are long, low, flat stretches faced seaward by an equally long, monotonous, sandy beach in which a scanty molluscan life is inferred from the stray shell fragments. Depression of the alternating areas has allowed the sea to encroach upon the land to the base of the low mountain ranges. Here rocky coasts and headlands with their minor sculpturing and drowned valleys take the place of sandy beaches and here shore life abounds. It is in these areas of depression that the corals are found. Their local occurrence is worthy of mention. In fracture planes the waves have excavated small caverns from a few feet to several yards deep. Many square yards of these caves are lined with incrusting corals such as Astrangia and Porites. None of these colonies except the reef-formers are ever subject to direct sunlight for more than a short time during, the day. They are some feet above low tide and out of reach of the local shifts of the sand. An occasional patch of dead corals, however, bears evidence that their calculation failed to consider all the vagaries of this destructive agent. In small baylets or in places protected from drifting sand occur small patches of a reef-forming coral, Pocillopora. In two localities some fifty miles apart, P. capitata var. robusta Ver., forms extensive colonies. One occurs near Puerto Angel where it forms a patch about twenty yards in diameter (Pl. II, Fig. 1). Individual colonies form hemispherical heads four feet or more in diameter. The colony is exposed at low tide only and as the fleshy parts are a dull earth brown it is never conspicuous. The branches in different parts of the head show distinct variations. Those on the part of the head not exposed to the force of the waves are round and have numerous branchlets, while those on the exposed side are flat or spatulate and but little branched. Near Escondido Bay, in a small inlet called Puerto Angelito, this species is so abundant that the aggregation may properly be called a reef. This inlet is some 500 feet wide and is so completely filled by coral that even small boats cannot enter. Coral fragments and coral sand make up a large percent of the beach material. The distribution of corals on the west and on the east coasts of Mexico and the flourishing condition of the two colonies mentioned indicate that temperature is not the exclusively controlling factor and that the presence or absence of rocky coasts is an equally important factor of control. But a word on the relationship of the Oaxaca corals. The genera are those common along the west coast of tropical America. The reef-forming coral, Pocillopora capitata, is closely related to Samoan and also to Hawaiian species. So close is this relationship that the species are separated on very small and unimportant details. It is possible that the northward distribution of the tropical species may be accounted for by near shore currents that transported the larvae. Evidence of these currents is afforded by the fact that some weeks after the terrific volcanic explosion of 1902 in Guatemala large amounts of pumice are reported to have been washed ashore along the Oaxaca coast. That this shore current, flowing northward and then westward along the southern Mexican coast, is constant, is indicated by the fact that pumice fragments are still being deposited along the strandline by the waves. DESCRIPTION OF SPECIES Pocillopora capitata Verrill var. robusta Verrill Pocillo pora capitata var. robusta Verrill, Conn. Acad. Sci. Trans., Two notable occurrences of this reef building coral have already been described. Porites panamaensis Verrill This species is a thin encrusting form and is not uncommon on rocky cliffs where it is protected from the rays of the sun. The fleshy parts are carmine in color. It also occurs in the Pleistocene. FIG. 1.-Astrangia browni Palmer n. sp. Holotype X 6. Palmer Collection. Recent. a, Fission, early stage. b, Fission, later stage. c, Fission, completed. d, Union of short septa with alternate long septa. FIG. 2.-Astrangia browni Palmer n. sp. Vertical section showing granular dentate septa and perforations of septa which produce the porous columella. X 6. |