. College collection of palaeontology. PTEROrODA. 117 CLASS PTEROPODA. Tliese small eeplialoiis niollnsks are named fi'om the resem- blance of their cliief organs of motion to a pair of wings. They are either naked, or provided with a delicate translucent sliell. In their first stages, they exactly resemble the gasteropod fry, and accordingly Lamarck, De Blainville and Owen regard them as a snb-class of the "•crawlers"; but CuVier, Woodward and Trj'on give them a higher rank. The shell, when existing, resembles either a univalve or a bivalve in which tiie two valves have been cemente
. College collection of palaeontology. PTEROrODA. 117 CLASS PTEROPODA. Tliese small eeplialoiis niollnsks are named fi'om the resem- blance of their cliief organs of motion to a pair of wings. They are either naked, or provided with a delicate translucent sliell. In their first stages, they exactly resemble the gasteropod fry, and accordingly Lamarck, De Blainville and Owen regard them as a snb-class of the "•crawlers"; but CuVier, Woodward and Trj'on give them a higher rank. The shell, when existing, resembles either a univalve or a bivalve in which tiie two valves have been cemented along the hinge. These " sea-butterflies," as they have been called, float in mid-ocean, forever out of sight of land, and are the food of northern whales and sea-birds. There are several hundred fossil species, some of them appear- ing: in the earliest Silurian or in the Cambrian, and being char- acteristic of the Silurian and Devonian. No. 307. Conularia Trentonensis, Hall. * This is one of the large,st and most extraordinary of the Pteropods. The shells are sometimes nearly a foot long. They are distinctly four-sided and finely striated with trans- verse lines. They occur in the Mesozoic. but are character- istically Palaeozoic, beginning in the earliest Silurian. About one hundred species are known. Trenton Limestone, Trenton Falls, N. No. 308. Tentaculites irregularis, Hall. This genus has been referred to the tubicular annelids, and its true position is still in question. It resembles the annelid Cornulites. The shell is a thm, straight conical tube, with numerous annulations or thickened rings. They are of small size, from a couple of lines to an inch in length. They occur in the Devonian, but are chiefly Silurian. In some strata the tiny shells are found in myriads. This slab, covered with specimens, is from the formation to which they have given the name Tentaculite Limestone (Upper Silurian), Schoharie, New York. *It may be necessary, in making up co
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