44 SECOND SUPPLEMENT TO THE CRAG MOLLUSCA. 



NucuLA TURGENS, S. Wood. 2nd Sup., Tab. V, fig. Q a, b. 



Sjjec. Char. N. testa ovato-rotundatd, ventricosd, tumidd,partim Icevigatdet partim con- 

 centrice costulatd ; 7nargine dorsali et ventrali convexiusculd ; margine intus denticulatd. 



Diameter |ths of an inch. 



Locality. Red Crag, Waldringfield. 



A single specimen of the genus Niicula is among Dr. Reed's specimens, kindly sent to 

 me for examination, which I have here had represented ; it has attached to it the name 

 of N. nucleus ? var. I think, however, it cannot be referred to that species, which is 

 much less inflated, and comparatively longer. The two valves are closely united, 

 and cannot be separated without endangering the integrity of the specimen. The shell 

 to which it seems to approach the nearest, from its tumidity, is N. sphenoides, Edwards, 

 an Eocene species, but that shell differs in shape, being more angular and elongated. 

 Our shell may be described as small, roundedly triangular, and very tumid, margin 

 crenulated (the margins, though the valves are adherent, disclosing this). The exterior, 

 which has been much rubbed, is smooth on the part nearest the umbo, but deeply ridged 

 on the part nearest the margin, and these ridges do not appear to be the result of 

 decomposition. Mr. Hancock has figured and described a shell under the name of N. 

 inflata, 'Ann. and Mag. Nat. Hist.,' 1846, p. 333, pi. v, figs. 13, 14, and this, Mr. 

 Hanley says, in his 'Monog. of the Nuculidse ' (p. 34, figs. 115, 110) is the same as 

 N. tenuis, Molier (as he has determined from the examination of his specimen), but as this 

 latter has a smooth margin and is more transverse than our present shell I am not able 

 to refer the latter to it, and have therefore given to it provisionally a new name. 



It may not improbably be a derivative specimen. 



Arca tetragona, Poli. 2nd Sup., Tab. VI, fig. 8 a, i; Crag. Moll., vol. ii, p. 76, 



Tab. X, fig. 1 ; 1st Sup. to do., p. 116. 



Locality. Cor. Crag, Sutton. 



The specimen 8 d now figured is given merely because it is that upon which the name 

 oiArca nodulosa, Miill., was introduced by Mr. A. Bell, into his list of Crag shells in the 

 ' Proc. of the Geological Association,^ vol. ii. It is now in the cabinet of Dr. Reed, and has 

 been sent to me by that gentleman with the proposed name oiArcapuella, A. Bell, attached. 

 I have had a small specimen of my own finding here also represented (fig. 8 a of Tab. VI), 

 which is very like it, and both, in my opinion, are specimens of A. tetragona, with coarser 

 ornament than usual. 



