BIVALV1A. 121 



21. Nucula Thanatiana, Edwards, MS. Tab. XIX, fig. 6. 



■ 



Spec. Char. N, testa ovato-trigond, convexiusculd, tenui,valde inaquilaterali, radialtm 

 striata; striis tenuibus, sub-decussatis ; lunula nulla aut indistinctd; ano piano, lavigafo ; 

 eardine crassiusculo, vmbonibus minimis; marginibus dor salt et ventrali conveasiusculis ; 

 moraine ventrali crenulatd. 



Shell ovately triangular, rather convex or tumid, thin, very inequilateral, and covered 

 with radiating striae ; striae fine and irregularly decussated ; no distinct lunule ; siphonal 

 or anal region flattish and smooth ; hinge rather thick, umbones small ; dorsal and ventral 

 margins slightly and nearly equally convex ; margins crenulated. 



Length, ^ an inch. 



Locality. Peg well Bay [Edwards). 



The figure above referred to was taken from an unique specimen in Mr. Edwards's 

 cabinet, of which the umbo was not quite perfect ; it represents the shell as rather more 

 elongated than it ought to be. 



22. Nucula tumescens, Edwards, MS. Tab. XVIII, fig. 1 a — c. 



Spec. Char. N. testa ovato-trigonuld, tumescent!, crassiusculd, lavigatd, obsolete 

 radiatd ; pedi-regionc sub-cuneatd; siphoni-regione brevissimd, truncatd ; umbonibus ter- 

 minalibus, depressis ; lunula indistinctd; marginibus crenulatis ; dentibus numerosis, ad 

 apicem decrescentibus. 



Shell ovately triangular and wedge-shaped, tumid, rather thick, and smooth ; pedal 

 region obtusely wedge-shaped ; siphonal region very short ; exterior obsoletely rayed ; 

 beaks terminal, depressed ; lunule indistinct ; anal region marked with an obtuse elevation 

 or ridge ; margins crenulated ; teeth numerous, decreasing towards the umbo. 



Length, \ an inch ; height, ^ths of an inch. 



Localities. Mead End, Barton (Edtvards). 



This is not rare. The principal distinction of the species is its great tumidity, thereby 

 giving more than ordinary depth to the interior of the umbonal region. 



23. Nucula Wethehellii, J. Sowerbg. Tab. XIX, fig. 9 a, b. 



Nucula Wetherellii. J. Sow. Geol. Trans., 2nd ser., vol. v, pi. viii, tig. 12, 1834. 



— Prestwich. Geol. Journ., 18-17, p. 105. 



— Morris. Catal. Brit. Foss., p. 218, 18.) 1. 



