PTEROPODA. 



389 



CLASS PTEROPODA. 



THE Class Pteropoda consists wholly of marine animals of small size, furnished 

 with a pair of fins at the sides of the head, by means of which they swim in the 

 open sea. The living forms are divided into two orders : the Gymnosomata and 

 Thecosomata. The Gymnosomata have no shells, and occur in such prodigious 

 numbers that they furnish food for whales and many sea-birds. The Thecosomata 

 have either straight or coiled shells, some of which are glassy in their texture and 

 very beautiful. It may well be doubted whether or not any of the Palseozoic fossils 

 belong to this order. They are referred to the following families : 



FAMILY ASPIDELLID^E. Aspidella. 



FAMILY CLATHROCCELIIDJE Clathrocoelia. 



FAMILY CONULARIID^. Conularia. 



FAMILY HYOLITHID^;. Coleolus, Coleoprion, Diplotheca, Hyolithellua, 



Hyolithes, Pharetrella, Stenotheca. 

 FAMILY MATTHEVIDJE. Matthevia. 

 FAMILY PTEROTHECID^. Pterotheca , 

 FAMILY ScENELLnxss. Scenella. 

 FAMILY TENTACULITID^;. Styliola, irentaculites. 



ASPIDELLA, Billings, 1872, Am. Jour. Sci., 

 3d ser., vol. 3, and Pal. 

 Foss., vol. 2, p. 76. [Ety. 

 aspidella, little shield".] 

 Small, ovate, bordered by a 

 narrow ring within which 

 it is concave ; in the middle 

 there is a ridge, from which 

 grooves radiate to the 

 border. Type A. terrano- 

 vica. 



terranovica, Billings, 1872, 

 Am. Jour. Sci., 3d ser., vol. 3, and Pal. 

 Foss., vol. 2, p. 77, Taconic. 

 Camerotheca, Matthew, 1885, Can. Rec. Sci., 



vol. 1, p. 149, syn. for Hyolithes. 

 oracilis, see Hyolithes gracilis. 

 CLATHROCOSLIA, Hall, 1879, Pal. N. Y., vol. 

 6, pt. 2, p. 203. [Ety. clathro, latticed ; 

 koilia, belly.] An oblique conical tube, 

 expanding more rapidly on one side 

 than the other; interior crossed by 

 unsymmetrical, arching, septal lines and 

 longitudinal ones, which give it a can- 

 cellated aspect; shell thin, translucent, 

 lamellose. Type C. eborica. 

 eborica, Hall, 1879, Pal. N. Y., vol. 5, pt. 



2, p. 204, Ham. Gr. 

 Clioderma, Hall, syn. for Pterotheca. 

 attcnuata, see Pterotheca attenuata. 

 expansa, see Pterotheca expansa. 



26 



COLEOLUS, Hall, 1879, Pal. N. Y., vol. 5, pt. 

 2, p. 184. [Ety. kokos, sheath.] Tubu- 

 liform, elongate-conical, straight or 

 slightly curved, 

 annulated, some- 

 times obli 



sometimes longi 



tudinally stri- 

 ated, interior smooth. Type C. tenui- 



cinctus. 

 acicula, Hall, 1843, (Orthoceras acicula,) 



Geo. Sur. 4th Dist. N. Y., p. 243, and 



Pal. N. Y., vol. 5, pt. 2, p. 187, Gen- 



esee Slate, 

 aciculatus, Hall, 1860, (Dentalium acicula- 



turn,) 13th Rep. N. Y. St. Mus. Nat. 



Hist., p. 107, Marcellus Shale and Por- ' 



tage Grs. 

 crenatocinctus, Hall, 1879, Pal. N. Y., vol. 



5, pt. 2, p. 188, Up. Held. Gr. 

 gracilis, Hall, 1879, Pal. N. Y., vol. 5, 



pt. 2, p. 190, Chemung Gr. 

 herzeri, Hall, 1888, Pal. N. Y., vol. 7, p. 



7, Waverly Gr. 

 Isevis, Walcott, 1885, Monogr. U. S. Geo. 



Sur., vol. 8, p. 199, Devonian, 

 mohri, Hall, 1879, Pal. N. Y., vol. 5, pt. 



2, p. 189, Up. Held. Gr. 

 spinulus, Hall, 1879, Desc. New Spec. 



Foss., p. 18, and llth Rep. Geo. and Nat. 



Hist. Ind., p. 322, Niagara Gr. 



