141 



PTEROPODA. 



No. 641. Bucania expansa, Hall. 



This loosely coiled, trumpet-mouthed shell is from the Tren- 

 ton Limestone (Lower Silurian) of Watertown, N. Y. 



Price, $0.40. 



No. 643. Strophostylus cyclostomus, Hall. 



From the Niagara limestone (Upper Silurian), Waldron, Ind. Price, $0.25. 



No. 643. Trails of G-asteropoda, 



From the Clinton group (Upper Silurian), New Hartford, N. Y. Price, $0.60. 



CLASS III.— PTEROPODA. 



These small Cephalous Molluscs are so called from the resemblance 

 of their chief organs of motion to a pair of wings. They are either 

 naked, or provided with a delicate translucent shell. In their first stages, 

 they exactly resemble the Gastropod fry ; and accordingly Lamarck, De 

 Blainville and Owen regard them as a sub-class of the Crawlers, but 

 Cuvier, Woodward, and Jones give them a higher rank. The active 

 Clio (the food of whales and sea-birds) has its head armed with 360,000 

 microscopic suckers — a prehensile apparatus perhaps unequalled else- 

 where in creation. The shell, when existing, resembles either a univalve 

 or a bivalve in which the two valves have been cemented along the 

 hinge. These " sea-butterflies," as they have been called, float in mid- 

 ocean in every latitude, forever out of sight of land. 



There are 32 fossil species, — all from the Tertiary, excepting the gi- 

 gantic Theca, and Conularia, which are Silurian. 



No. 644. Conularia undulata, Conrad. 



The Conularke. are commonly referred to this Class ; hut 

 their large, thin, pyramidal shells, chamhered at the apex and 

 admitting of some motion at the angles above, present some of 

 the distinctive features of Cephalopods. If really pteropodous, 

 they were the giants of the Class. The angles of the Conularia 

 are grooved, and the sides are striated transversely. This speci- 

 men is from the Hamilton group (Devonian), Cazenovia, N. Y. 



Price, $0.40. 



No. 645. Conularia . 



From the Upper Silurian of Bohemia, and now in the Ward Museum. Uni- 

 versity of Rochester. Price. $0.60. 



