JURASSIC FOSSILS. 41 



FAMILY TEREBRATULIDiE. 

 Genus TEREBRATULA, Miiller, 1776. 



Tekebratula . 



PI. 8, Pig. 2, and 2 a, b. 



Shell subovate, gibbous, greatest convexity at or a little be- 

 hind the middle ; front faintly sinuous on each side of the slightly 

 truncated middle. Ventral valve much more convex than the 

 other posteriorly ; forming a regular semi-ovate curve from near 

 the beak to the front, where there is no mesial sinus, but some- 

 times an exceedingly faint longitudinal furrow on each side, cor- 

 responding to slight elevations in the other valve ; anterior mar- 

 gin a little produced, so as to fill a shallow flattened recess in the 

 edge of the other valve. Umbo gibbous, and rounding in on 

 each side without defined lateral angles (point of the beak, in the 

 only undistorted specimen in the collection, broken away). Dor- 

 sal valve less gibbous, and much shorter than the other, owing to 

 the prominence and convexity of the umbo of the latter ; forming 

 a regular gentle arch from the beak to the front, where there is 

 a low flattened mesial prominence, with a slight concavity on 

 each side of it. Surface with moderately distinct concentric 

 marks of growth. 



Length, about 1.45 inch ; breadth, 1 inch ; convexity, 0.85 inch. 



This shell bears considerable general resemblance to some varieties of T. pero- 

 valis, Sowerby ; but is proportionally narrower, and has the umbo of the ventral 

 valve much more gibbous, and more prominent, as well as less angular on each 

 side. It would be idle, however, in a genus like this, to pretend to identify a 

 species, from two or three mutilated and distorted specimens, with any known 

 form ; nor is it desirable, under such circumstances, to name it as a new species. 

 It is more than probable, however, that it will prove to be new when a good series 

 of specimens can be examined. 



PAL. VOL. I. — 6 



