48 MOLLUSCA FROM THE CRAG. 



Our shell is not strictly ovate, but more of an oblong form, with the angles rounded 

 off ; the sides being somewhat straight, or of very gentle curvature, it is tumid and 

 thin ; the whole of the ribs being visible on the inside, they occupy the centre of the 

 shell, and are distributed over about half the surface, two or three of the middle ones 

 being the most distinct, and these are more conspicuously so on the inside ; umbones 

 prominent and divergent, leaving a wide ligamental area between them, thereby 

 enabling the animal considerably to divaricate the valves ; costse obtusely angulated, 

 rough, but not imbricated, showing distinct lines of growth ; hinge-line straight ; 

 cartilage pit concave, projecting inwardly, forming an angle of 90, and occupying 

 nearly half the ligamental area. The shell extends on each side of the umbo into 

 what are called auricles, the greater part of which space is occupied by the ligament ; 

 on the inside beneath these auricles the shell is thickened and strengthened by a 

 prominent ridge, diverging from beneath the umbo towards the sides : in some speci- 

 mens may be seen the impression of the large adductor muscle inclining towards the 

 centre ; my largest specimens do not exceed half an inch, measuring from the umbo 

 to the ventral margin, and the transverse diameter about half that size. 



A specimen from the ./Egean Sea was given to me by Professor E. Forbes, with the 

 name of L. elongata, which so much resembles some of the Crag specimens (fig. 3, c), 

 that I have introduced the name among the synonyma. In the ^Egean shell, which 

 was obtained from the depth of 100 fathoms, the costated striae are in number 

 about 20, more distinct and distant on the centre or convex portion, and of course 

 widest near the margin, not rounded but angulated ; while in the generality of speci- 

 mens of subauriculata they are rounded, but the same characters of sharpened costse 

 are visible in some of the Crag specimens, and there is not a distinction between the 

 two sufficient, in my opinion, for specific separation ; probably with a large number of 

 individuals of the ^Egean shell, as much difference might be detected as is exhibited 

 in my Crag specimens. 



Upon some of the smaller and most perfect specimens of this species from the 

 Crag, may be observed a row of fine crenulations, occupying the entire edge of the 

 hinge-line (fig. 3, 6), being a miniature representation of what has been considered a 

 good generic character ; these are, however, so small as to be of little service for the 

 ordinary purposes in which the teeth or prominent portions of the shell about the 

 hinge are employed by the animal. 



LIMA OVATA, S. Wood. Tab. VII, fig. 5. 



LIMATULA OVATA. 8. Wood. Mag. Nat. Hist., New Series, vol. iii, p. 235, pi. 3, fig. 5, 

 1839. 



Spec. Char. Testa minutd, ovatd, aequilaterd, undigue clausd, inflatd; in mediis 

 costatis, utrinque obsoletis, costis angulatis circa septem ; cardine recto, foveo ligamenti 

 trigond, concavd. 



