CO^CHYLlk—DITHYRA. 5. 23 



In rocUs in the Isle of Sky. 



We are unacquainted with this shell, except from the descrip- 

 tion of Montagu. It appears to resemble the Saxicava rugosa' 

 but the anterior side is more dilated, and the striae are more or less 

 raised into ridges. 



5. HIATELLA— l>/lt/l>/iV^. 



Te»ta transversa ina^qtiiimlcis, inaquilaterlis, margine stipero 

 vel latere antico hiante. Cardo dente unico inter duos ohso- 

 letos penetrante : lateralihus nullis. Ligamentum externum 



Shell transverse, inequivalve, inequilateral, open at the upper 

 margin or anterior end. Hinge with a single tooth in one valve 

 closing between two obscure ones in the other: lateral teeth 

 none. Ligament external. 



Of the two subsequent species we have not thouglit it necessary 

 to form different genera, merely from the variation in tlieir habi- 

 tats and openings. Tlie first is, we believe, generally attaciied 

 to the rugged cavities of oysters, and the roots of Fuci, by a strong 

 byssus issuing from the opening in the upper or front margin. 

 The other is imbedded in rocks, and like most of the rock shells 

 opens at the anterior or smaller end. 



