PROCEEDINGS OF THE NATIONAL MUSEUM. 433 



subsidence. It con tinned until only tlie summits of the mountain 

 chains were above the level of the sea, and probably reached its culmi- 

 nation sometime in the Miocene period. During- this time such groups 

 of terrestrial and Huviatile mollusks as then existed were driven higher 

 and higher up the mountain sides, and crowded into ever-narrowing 

 quarters, and it is quite probable that some of the genera and many 

 species were drowned out or j)erished for want of room and food. As 

 Puerto Rico consists mostly of low, comparatively level land, witli a 

 single notvery lofty mountain range, it is possible that the limited area 

 left above the sea accounts for the absence of many genera finind in the 

 other islands, and which may have been abundant within its borders at 

 the time of a former laud connection. 



During a visit to Jamaica the past winter the writer, in company 

 with Mr. John B. Henderson, jr., of this city, obtained three large boxes 

 of fossil marl, which we dug from a bed some two feet iu thickness, in 

 what is called the White Limestone Series of the Miocene at Bowden, 

 near the east end of the island. This marl, whicfn was brought to the 

 Smithsonian Institution, has proven to be astonishingly rich in fossils, 

 es])ecially marine mollusca, an<l in it were found six species of land 

 shells, consisting of a FtychocochUs, a LucUlella, a Pleurodonte, a Thy. 

 sanophora, an Opeas, and a Succinea. The first two and the last named 

 were in good condition, and nearly perfect; the Pleurodonte was repre- 

 sented by two fragments, an apex with three whorls, and an aperture 

 containing the teeth. The Thysanophora was iu a crumbling condition 

 and the two si^eciraensof Opeas were broken. At Bogwalk, at the foot 

 of a Miocene limestone ledge, the writer found fragments of fossil Sagdas, 

 but not ill a condition for identification. These shells were no doubt 

 washed down by rains and streams and deposited in the marine strata, 

 as we found in several cases an abundance of recent forms in the bays 

 and thrown up along the shores. I consider the evi deuce of these fossil 

 land shells with regard to the past history of the groups, and of the 

 Greater Antilles, quite important. They show that in the Miocene 

 period, at a time when perhaps all but the summits of these islands was 

 submerged, several of the great characteristic groups of this region 

 were iu existence; that no change whatever has taken place in their 

 characters beyond the differentiation of species; for, with the excei)tion 

 of the Succinea, which doe^: not seem to differ from *V. latior, an abun- 

 dant species on this -land, and the Opeas [0. striata, also very common) 

 all these forms are probably extinct. The Bowden beds are believed to 

 be the equivalent of the Cliattahoochee formation of the southeastern 

 United States, and were no doubt laid down in the earlier part of the 

 older Miocene. The stratum from which these fossils were dug is only 

 a i'ew feet above sea level, and is overlaid with shales and marls to the 

 summit of the hill, some 300 feet above. Succinea is world-wide as well 

 as Opeas, and neither are distinguished in the West Indies by any 

 special characters. Thysanophora is distributed throughout the Greater 

 Proc, N. M. 94 28 



