50 
GASTROCHiENA contorta. 
TAB. DXXVI. —Jig. 2. 
Spec. Char. Sheath clavate, bent nearly at a 
right angle : valves ovate-elongated, marked 
with very slender stride ; the sinus between 
them wide, oval, pointed. 
Syn. Fistulana contorta. Deshayes Cocquilles 
Fossiles , v. 1. p. 16. pi. 1. Jig . 24, 25, & 27. 
Mem. de la Societe d’Hist. Nat. v. 1. pt. 2. 
p. 251. n. 3. pi. 15. f. 4. 
This species exhibits all the characters of the genus, 
forming a sheath that is more or less imbedded in other 
shells ; and the aperture of which, produced and often 
bent, is partially divided by two opposite ridges : the 
general form of the valves, especially the width of their 
anterior extremities, and the fine striae upon their sur- 
face, distinguish it from other species. The form of the 
sheath depends so much upon its situation, that it is not 
safe to lay any stress upon it as a specific character : we 
admit it, however, as it has been employed by Mons. 
Deshayes. 
By no means unfrequent in other fossil shells of co- 
temporary formation with those of the London Clay. 
The specimens figured are from Barton. From the larger 
size of some empty sheaths which are upon the same 
specimens, we suppose the shells are sometimes much 
larger than those figured. 
The five large figures are magnified representations. 
At letter a is seen the external portion of a sheath. 
