1847.] SHARPE ON THE PALHZOZOIC ROCKS OF N. AMERICA. 171 
HETEROPODA. 
Species. References and Synonyms. Strata. Localities. |Found in Europe. 
BELLEROPHON. 
bilobatus ...... Sowerby, Sil. Syst. t. 19, f.;Blue limestone. |Cincinnati. {Lower Silurian 
13; Emmons, Report, p. formation. 
392, f. 6; Hall, Palezont. 
NE ©. te.40)f 3: 
profundus ...... Euomphalus sp.Conrad,Ann.|Pentamerus Schoharie. 
Report, 1839, p. 62; Va-| limestone. 
nuxem, Report, p. 117, 
f. 2; Mather, Report, p. 
346, f. 2; Hall, Report, 
App. t. 27, f..2. 
PoRCELLIA. 
ornata (16) ...|Cyrtolites sp. Conrad, Ann.|Hudson’s River |Salmon River,|Lower Silurian 
Report, 1838,'p.118; Em-| group, Blue Cincinnati. | form., near 
mons, Report, p. 402, f. 2.| limestone. Capel Cerrig. 
CEPHALOPODA. 
ORTHOCERAS. 
articulatum ...|/Sowerby, Sil. Syst. t. 5,/Hamilton group. |............cec00 Ludlow form. 
f. 31. 
Notes on some of the species contained in the preceding list. 
(1) Avicuta.—The palzeozoic species of this genus cannot be de- 
termined easily : their horny shells have suffered much from a scaling 
off during decay, which has frequently altered their outline and thus 
added to the difficulty caused by their original variations of form: 
moreover the rocks in which they are most common do not admit of 
their perfect preservation. From want of attention to these circum- 
stances the species have been extravagantly multiplied. Mr. Conrad 
has described as species many which it is impossible to distinguish, 
and in some instances has increased the number by describing sepa- 
rately each valve of the same species*. It would require a larger 
collection of specimens than is at my command to enable us to limit 
all the species properly. The following species are found both in 
England and in America, and have not yet been published here :— 
(2) Avicuta Boypi1, Conrad.—“ Subrhomboidal, compressed, 
lower valve with numerous radii, disposed to be interrupted by con- 
centric lines, which are fimbriated, or have numerous angular in- 
dentations ; anterior wing short, sinuous, truncated ; posterior wing 
ample; posterior extremity of the valves acutely rounded+.” 
This species has some resemblance to 4. rectangularist, from 
which it differs in a less development of the anterior part of the shell 
and in being more oblique ; moreover it is a true Avicula, and the 
A, rectangularis is probably of the genus Pterinea. Found abun- 
* Journal of the Acad. Nat. Sciences of Philadelphia, vol. viii. 
t+ Conrad, Journ. Acad. Nat. Sci. Phil. vol. viii. p. 237, and t. 12. f. 4. 
¢ Sil. Syst. t. 3.f. 2. 
