92 HYALEID^. 



Hyolithes, Eicliw., 1840. 



Syn. — Tlieca, Morris, 1845. Pugiunculus, Barrande, 1847. 

 Cleidotheca and Centrotheca, Salter, 1866. 



Distr. — Fossil, 40 sp. Palseozoic ; North America, Europe, 

 N. S. Wales. H. fasciculatus (xlii, 11). 



Shell straight, conical, tapering to a point, back flattened, 

 aperture trigonal. Length, 1-8 inches. 



HYOLiTHELLUS, Billings. Differs from Hyolithes in its long, 

 slender form and in the peculiar structure of the operculum. 

 H. micoMS, Billings (xlii, 12). Palseozoic ; IS". America. It may 

 be a Salterella. a represents the rate of tapering of the shell 

 on its ventral side, and the included figiire its apical portion ; b 

 is the inner surface of the operculum, enlarged 2-1, showing 

 radiating muscular impressions. 



CLATHROCCELiA, Hall, 1879. Shell thinner than Hyolithes, 

 interior cancellated by longitudinal striae crossing the arcuated 

 septal lines. H. Ehorica^ Hall. Devonian ; U. S. 



Pterotheca, Salter, 1852. 



Syn. — Clioderma, Hall, 1861. 



Distr. — P. transversa^ Portlock. 8 sp, Silurian ; Ireland, 

 Wales, Canada, Bohemia. 



Shell bilobed, transversely oval, with a dorsal keel projecting 

 slightly at each end ; ventral plate small, triangular. 



CYRTOTHECA, Hicks. Shell with curved apex ; a longitudinal 

 ridge extends along the surface of the sides near the centre ; but 

 the surface is otherwise tolerably smooth ; mouth funnel-shaped 

 with one lip greatly elongated. P. hamula, Hicks (xlii, 13). 

 Cambrian ; Gt. Britain. 



STENOTHECA, Hicks. Curved, wide, with the lines of growth 

 strongly marked on the surface. P. Cornucopiae, Hicks (xlii, 14). 

 Cambrian ; Gt. Britain. 



SCENELLA, Billiugs. Has a smoother surface. Palaeozoic ; New- 

 foundland. 



Phragmotheca, Barrande, 1867. 



Distr. — P. Bohemica, 'Ba.rrande. Upper Silurian ; Bohemia. 



Shell like that of Pterotheca, but having septa. Differs from 

 the cephalopods, which are chambered, in the want of a siphuncle. 



CoNULARiA (Miller), Sowerby, 1818. 



Etym. — Gonulus., a little cone. Syn. — Conulites, Schloth. 



Distr. — Fossil, about 100 sp. Silurian to Carb. ; N. America, 

 Europe, Australia. G. Geroldsteinensis (xlii, 15). 



Shell four-sided, straight, and tapering, the angles grooved, 

 sides striated transversely, apex partitioned off. The Conularise 

 were the giants of the Pteropoda ; G. inornata, Dana, of Aus- 

 tralia, is supposed to have been 16 inches long. 



