INSTITUTE OF SCIENCE, PHILADELPHIA. 167 



Bay, in a water-worn sandstone of yellowish brown color, by Messrs. Willcox 

 and Ball. 



This species is the largest fossil form from the United States except C. 

 carolinensis, which is a much thinner and lighter shell, with a wider and less 

 uniform aperture, recalling that of C. miis L. With it were found small in- 

 ternal casts recalling C. pingiiis, but the fossils in this particular ledge are so 

 poorly preserved for the most part as to be hardly identified with absolute 

 confidence. C. Willcoxii reaches a length of 64.0, and a width of 42.0 mm. 

 The specimen figured has suffered a little at the lower end of the aperture, fig- 

 ure 12 c, in the process of cutting out the matrix. 



Subgenus Siphocyprsea Heilprin. 

 Siphocypma Heilprin, Trans. Wagner Inst. i. p. 86, 18S7. 



This remarkable form of Cyprcsa differs from all other species recent and 

 fossil in the prolongation of the posterior commissure of the aperture by a 

 comma-shaped sulcus coiled over the apical region. This would indicate 

 either a central filament at the junction of the expanded halves of the mantle, 

 thus preventing the usual deposition of callus at that point, or a double spiral 

 prolongation at this part of the margin of the mantle. It is unlikely that 

 the position of the respiratory siphon differed from that of other Cyprsas, as 

 the form of the young shell does not lend itself to this hypothesis. It is more 

 probable that we have to do in this case with a unique and special case of 

 modification and development at the posterior sinus. 



Cyprsea (Siphocyprasa) problematica Heilprin. 



Plate 5, figures 10, 10 b. 



Siphocyprtsa problematica Heilprin, op. cit. pp. 87, 133, pi. iv. figs. 12, 12 a, 12 b, pi. xvi. a, 



fig- 73- 



The young shell which I have figured, as above mentioned, instead of ex- 

 hibiting a pointed spire like most Cypraeas, after the first three whorls shows 

 an apical, cup-shaped depression, exhibiting the volutions, in the centre of 

 which the nuclear tip appears a little elevated. The last whorl rises more and 

 more until the animal commences to form its thickened lip. The posterior 

 extremity of the right lip is first thickened, and the callus curves to the left 

 and upward. At the same time a callous deposit is made on the body oppo- 

 site and parallel to the first-mentioned. The deposition continues on both 

 sides, the right side for some time getting the larger share, but after a time 

 the deposit ceases or becomes less rapid on the right and more so on the left. 

 The left-hand wall of callus finally overshadows the curved projection on the 

 right, and the latter is frequently somewhat resorbed at the tip, while the wall 

 representing the outline of the head of the " comma " becomes very promi- 

 nent and almost tubular. The adult shell varies in form from slightly pyri- 

 form to subcylindrical ; the basal callus is but little flattened or expanded 



