80 PROCKEDINGS OP THE ACADEMY OF 



with oblique, slightly archcnl lines of growth, which, on the first 

 and second turns of the spire, are rather coarse, well defined, and 

 present the characteristic regularity of size and arrangement, but 

 soon become, on the succeeding turns, much finer and more 

 crowded, as well as occasionally interrupted by irregular, stronger 

 furrows and wrinkles of growth. 



Height of a medium-sized specimen, 1.10 inches; breadth, 1.50 

 inches ; height of aperture, measuring at the margin of the lip, to 

 the top of the angle above, 0.95 inch ; breadth, about 0.87 inch. 



It is possible that this may be the full-grown adult form of Isone- 

 ma Jepressa, M. & W., as its first and second volutions have much 

 the form and surface markings of that shell. Still, as it shows 

 only the same number of volutions in specimens of nine or ten 

 times the volume of the typical specimen of that species, 1 am 

 led to believe it distinct. Although young specimens are more 

 inclined to be subangular around the middle of the outer turn 

 than in the adult, which often has the body whorl regularly 

 rounded, I think it is never at any stage of growth so angular as 

 in the /. depressa. 



In large examples, with the strong striae of the fii'st turns of 

 the spire obscured by ei'osion, the specimens of this shell (which 

 are usually preserved in such a condition as to present a perfectly 

 white chalk appearance), when viewed from above, resemble very 

 much the bleached shells of some of the large depressed forms 

 of Hdicidse. The strongly flattened, smooth inner lip, however, 

 gives a very different expression to the under side. 



Until more is known in regard to the texture and ornamenta- 

 tion, and particularly in regard to the nature of the inner lip, in 

 the shells on which the genus Holoj)ea was originally founded, it 

 is scared}'' possible to determine exactly the relations of our 

 shells to that group. My present impression, however, is that 

 they constitute a distinct genus. 



The species here described resembles some forms of Platys- 

 chisma, McCoy, but they show no traces whatever of the shallow- 

 sinus of the outer lip, and differ remarkably in the presence of 

 the thickened, appressed, and distinctly flattened inner lip, while 

 in the species here described, and in /. depressa, there is not 

 even a slight umbilical perforation. This latter character, how- 

 ever, may not be constant in the group. 

 Locality and position. Same as foregoino-. 



. [June 6j 



