18 \ MOLLUSCA FROM THE CRAG. 
lamellated costze of the exterior. One peculiarity, observable in this shell, is the very 
small portion of surface by which it was attached, its own substance and weight 
seeming sufficient security against displacement by the movement of the water. 
The form of its muscular impression is elongato-ovate across the shell, differing in 
no respect in that character from the form displayed by the same muscle in specimens 
undoubtedly belonging to edulis. The upper valve is quite flat, very thick, and only 
faintly marked with radiations, scarcely visible in the younger state, and on each side 
of the ligamental area, upon the edge of the shell, are some denticulations like those 
visible upon the same valve of edw/is in the same place. 
Hinnites.* De France, 1821. 
Hrynita. Ferussac. 1821. Gray, 1826. 
Hinnites. J. Sow. 1827. 
Hinnus. Jd. Sow. 1835. 
Hynnites. Herrn. 1846. 
Generic Character. Shell inequivalve, subequilateral, more or less ovate, thick, and 
strong, covered externally with somewhat irregular, squamose, or radiating coste. 
Valves eared with a deep and elongated area for the ligament or cartilage, which is 
wholly internal; a large ovate impression by the adductor muscle, that by the mantle 
entire. 
ANIMAL UNKNOWN. 
This genus was first established by M. de France, in the ‘Dict. des Sci. Nat.,’ 
tom. xxi, p. 169, upon a fossil species, which appeared to unite the characters of the 
two genera, Ostrea and Pecten, differing from the former in adhering by its outer 
surface, only in its older state, and by the opposite valve: while in the young it was 
probably fixed by a byssus. It has, by some authors, been united with Pecten since one 
species of that genus (P. puszo), is in the young state fixed by a byssus, but when more 
grown, becomes attached by the outer surface of its right valve in the same manner. 
This peculiar habit is here considered as alone insufficient for excluding the present 
genus, as the extreme solidity of two or three fossil species of typical characters, with 
a peculiar form in the muscle mark, seem to indicate a difference in the animal 
inhabitant sufficient to remove them from Pecten. 
In the juvenile state the form of the shell is very similar to that of Pecten with 
its projecting auricles, and an opening or sinus beneath the anterior one in the right 
valve through which, in all probability, there issued a byssus ; as it advanced in age 
its habits became altered, when it fixed itself by the outer surface of its valve. This 
same habit is adopted by P. pusio in the recent state, though not so in the fossil form 
of what is considered as the same species in the Crag Formations, where they never 
* Etym. ¢yvos, hinnus, vel vyvos, vomer, sec, Herrm. 
