92 HYALEIDA. 
HyouiruHes, Hichw., 1840. 
Syn.— Theea, Morris, 1845. Pugiunculus, Barrande, 1847. 
Cleidotheca and Centrotheca, Salter, 1866. 
Distr.—Fossil, 40 sp. Paleozoic; North America, Europe, 
N.S. Wales. A. 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. micans, Billings (xli,12). Paleozoic; N. America. It may 
be a Nalterella. a represents the rate of tapering of the shell 
on its ventral side, and the included figure its apical portion; 6 
is the inner surface of the operculum, enlarged 2-1, showing 
radiating muscular impressions. 
CLATHROCHLIA, Hall, 1879. Shell thinner than Hyolithes, 
interior cancellated by longitudinal strive crossing the arcuated 
septal lines. HA. Hborica, 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 (xlhi, 13). 
Cambrian; Gt. Britain. 
STENOTHECA, Hicks. Curved, wide, with the lines of growth 
strongly marked on the surface. P. Cornucopix, Hicks (xlii, 14). 
Cambrian; Gt. Britain. 
SCENELLA, Billings. Has asmoother surface. Paleozoic; New- 
foundland. 
PHRAGMOTHECA, Barrande, 1867. 
Distr.—P. Bohemica, Barrande. Upper Silurian; Bohemia. 
Shell like that of Pterotheca, but having septa. Differs from 
the cephalopods, which are chambered, in the want of a siphuncle. 
ConuLArtA (Miller), Sowerby, 1818. 
Etym.—Conulus, a little cone. Syn.—Conulites, Schloth. 
Distr.—Fossil, about 100 sp. Silurian to Carb.; N. America, 
Europe, Australia. C. Geroldsteinensis (xi, 15). 
Shell four-sided, straight, and tapering, the angles grooved, 
sides striated transversely, apex partitioned off. The Conularize 
were the giants of the Pteropoda; C. inornata, Dana, of Aus- 
tralia, is supposed to have been 16 inches long. 
