298 LIOTIIDiE. 



which is widest in the middle of the edge ; nucleus obscure, 

 punctured. 



PARIA, Gra}^ Shell elliptical, mouth wide ; inner lip flat, 

 shelving upwards, produced and truncated in the middle, with a 

 roundish notch on .'each side near the margin of the cavity. 

 Operculum, shelly plate subquadrangular, lower edge straight, 

 transverse, with a flexible flap, the upper edge with two lobes, 

 the marginal lobe elongate, linear. 



STENOPOMA, Gray. Shell elongate ; mouth elongate, narrow. 

 Operculum oblong-elongate, the horny part triangular, very 

 oblique, acute near the nucleus, and rounded at the end ; shelly 

 plate elongate,. thin, with two elongated ridges on the upper end, 

 the marginal one produced into a spine, with a notch on its left 

 margin. 



ORTHOPOMA, Gray. Operculum oblong; horny part triangular, 

 rather oblique ; shelly plate half oblong, rather narrowed above, 

 and rounded at the upper edge, with a very slight fold diverging 

 from the nucleus to the left upper margin ; the anterior carti- 

 laginous flap large, broad. Shell unknown. 



The characters of all these divisions so run together through 

 a series of specimens that they may be regarded as practically 

 worthless. 



Yelates, Montfort. 



Distr. — Tertiary. V. perversa, Linn. (Ixxviii, 81, 82). 



Shell oval-conic, spiral at the apex only ; last whorl greatly 

 enlarged, resembling Trochita in shape ; apertvire basal, semi- 

 circular, forming with the wide flat, shelf-like columellar lip a 

 circular outline ; columellar lip dentate. 



VELATELLA, Meek, 1878. Cretaceous and Laramie ; United 

 States. V. carditoides, Meek (Ixxviii, 85, 86). 



PiLEOLUS (Cookson), J. Sowerby. 



Etym. — Pileolus, a little cap. 



Distr. — Marine ; only known as fossils. 



Shell limpet-like above, with a subcentral apex ; concave 

 beneath, with a small semilunar aperture, and a columellar disk, 

 surrounded by a broad, continuous peristome. 



The secondarj^ species have the basis generally rounded and 

 the apex subcentral, while the tertiary species have it more oval 

 and the apex terminal ; to the latter, approaching more nearly 

 the recent Navicellae, Deshayes applies the subgenerie name 

 TOMOSTOMA. P. radiatus, d'Orb. (Ixxviii, 83, 84). 



Family LIOTIID^. 



Shell depressed spiral, white, ribbed, sometimes cancellate, or 

 nodulous ; aperture orbicular, rarely pearly within. Operculum 

 corneous inside, outside having a calcareous coat formed of 

 separate, pearl-like, shelly particles placed in spiral lines. 



