GAsTEROPODA. | UPPER PALAZOZOIC MOLLUSCA. 528 
6th Order. PrcTINIBRANCHIATA. See page 289. 
2nd Family. CREPIDULIDZ. See page 289. 
Genus. CAPULUS. See page 289. 
CaPULUS AURICULARIS (Mart. Sp.) 
Ref: and Syn. = Conch. Helicites auricularis Martin, Pet. Derb. t. 40. f. 3, 4.= Pileopsis vetustus ? (Sow.) Phill. 
Geol. York. Vol. II. t. 19. (mot of Sowerby);?+P. angustus Phill. ib. f. 19?+P. neritoides Phill. ib. 
f. 16 to 18. 
Desc.—Discoid, tumid, periphery obtusely angulated, rounded ; spire gibbous, of very variable size, spirally 
inrolled to the right side, of one and a half volutions, not projecting beyond the tumid boundary of the depressed 
suture of the body-whorl; mouth elongate, oval, oblique (left side highest), slightly expanded or reflected on 
the left side, forming there an imperfect, oblique umbilicus ; edge broadly and irregularly sinuated. Surface 
with moderately strong, irregularly sinuous, transverse lines of growth, crossed on the left or umbilical side by 
a few obtuse, obscure, longitudinal or spiral strize. Diameter of average specimen one inch, proportional width 
of last whorl varying from = to 4 according to the size of the spire, thickness of last whorl =. 
As M. de Koninck has well observed, this species is strongly distinguished from the P. vetustus (Sow.) by 
the much greater size, tumidity, and perfect enrolment of the oblique spire. The proportion which the spire 
bears to the whole diameter is very variable. I have observed the spiral striz on the base, alluded to by 
Mr Phillips in his description of his P. xeritoides, obscurely on parts of one of our specimens. None of the 
modern writers seem to have noticed the description and figures of Martin, which well represent two varieties 
in size of the spire. 
Position and Locality —Not uncommon in the carboniferous limestone of Derbyshire. 
Genus. METOPTOMA (Pihiil.) 
Gen. Char.—Shell depressed, conical, very slightly inequilateral, left side steeper and smaller than the 
right, truncated behind, and the apex inclined backwards nearer to the posterior than the anterior end; base 
truncato-elliptical or subtrigonal. Muscular impression horse-shoe-shaped, with dilated pyriform ends extending 
searcely halfway to the front, surrounding the truncated posterior end; margin in one plane except in the 
middle of the posterior end, where it is raised, with a more or less distinct sinus. 
The position of the muscular impression marks the posterior end, and shews that the apex is directed 
backwards and near the posterior end, the reverse of what is found in Patella, as M. de Koninck has already 
noticed in the supplement to his Animaua Fossiles. The same characters convince me that the proper place 
for the genus is near Capulus, in which all these characters are seen, and which in fact only differs from 
Metoptoma in having the apex more inrolled, and the lateral edges less regular, and no distinct truncation. 
On this view there would be no evidence, from these fossils, for the occurrence of the Cyclobranchiate mollusea 
in the Paleozoic rocks, as it is now obvious they should be arranged with the recent and Paleozoic Capuli in 
the Pectinibranchiate order. 
METOPTOMA ELLIPTICA (Phill.) 
Ref. and Syn.—Phill, Geol. York. Vol. II. t. 14. f. 9.= Patella elliptica de Kon. Anim. Foss. Belg. 
t. 23 bis. fig. 3. 
Desc.— Elongate-oblong, elliptically rounded in front, truncated and very slightly dilated at the lateral 
angles behind; middle of the posterior margin slightly notched by a broad, moderately deep, doubly angulated 
