44 SYNOPSIS OF THE CHARACTERS OF THE 



DmiNus. M'Coxf. 



Qen. C^.— Patclliform; apex perforated by two oval foramina, symmetrically placed, one on the right 

 side, the other on the left. 



This most extraordinary genus is nearly related to the recent Fissurella of Lamarck; but Instead of the 

 single dorsal, branchial opening of that genus, we have here two distinct, oval foramina, laterally placed vrith re- 

 spect to the apex, they are separated by a distinct, narrow, flattened septum. In some of the recent species of 

 Fissurella, the opening is contracted in the middle, so as to indicate an approach to the structure here noticed. 

 Only one species is as yet known to me. 



DmiNus BucKLANDi. MCoy. (PL V. fig. 28). 



Sp. CA.— Obovate, conical, depressed; apex prominent, obtuse, inclining forward one third the length 

 from the anterior margin; surface slightly irregular; smooth, or with a few lines of growth near the margin. 



This very curious little shell is obtusely trigonal in its outline, the front being obtusely rounded ; the 

 posterior margin truncated; lateral angles rounded; the posterior and lateral margins are about equal in length. 

 Length five lines ; width five lines ; height one line and a half; foramina three-fourths of a line in length, half 

 their length distant from each other. 



ACROCULIA. Phil^ 



Qgj^ Q]^ siiell obliquely spiral; spire dextral; mouth large; no columella; a deep, wide notch in the 



right lip. 



ACROCULIA ANGUSTATA. PJul. SP. 

 Pileopsis angustus. Phil. Geol. York. 



gp_ Qji_ Apex spirally involute, narrow; mouth expanded; delicately striated across. 



The transverse striae are exceedingly fine, the surface appearing smooth to the naked eye ; the spire is 

 more perfectly formed than in any of the other species, and the mouth is dilated, the whole form approaching to 

 that of the Natica ampliata, Phil, wliich Goldfuss places in the present genus. Length nine lines, width of 

 the mouth six lines. 



ACROCULIA CAN^VLICULATA. M'Coy. (PI. III. fig. 13). 



Sp_ Ch. — Subcorneal, compressed; apex oblique, incurved; aperture deeply sinuated, trilobate; from each 

 of the projecting lobes a deep channel extends to the beak, one passing up the back, and one in the middle of 

 each side ; there are a few irregular minor sulci parallel to the principal channels. 



The trilobate aperture approximates this species to the A. triloba, Phil., but the apex is more oblique, and 

 the deeply channeled surface distinguish it equally from that, and from the other described species ; the right 

 lateral furrow is deeper than the left. Length nine lines, width five lines. 



ACROCULIA CARINATA. M'Coy. 

 Pileopsis cassideus. D'Archiae and De Verneuil. 

 Sp. Ch. — Obliquely conical; apex free, incurved; very much compressed ; back sharply keeled ; surface 

 smooth. 



* Etym. Ji?, double, and pivs?, the nostrils, in allusion to its double breathing holes. 



b Although the uaiiic Platyceras of Conrad has the priority over the term Acroculia, yet the former seems so singu- 

 larly inappropriate, that I have retained Professor Phillips's name, which has been already extensively adopted by Euro- 

 pean writers. 



