48 SECOND SUPPLEMENT TO THE CRAG MOLLUSCA. 



upon which that name as a variety of T. papyracea had been introduced into the list by 

 Mr. A. Bell in the 2nd vol. of the ' Proceedings of the Geol. Association,' I have had it 

 figured as above (6 b), and with it one of my own from the same locality, exhibiting 

 the ordinary form of papyracea (6 a). 



T. villosiuscula is considered both by Forbes and Hanley and by Dr. Jeffreys as a 

 variety of papyracea, as being more equilateral than the typical form of that species, but 

 the specimen sent me by Dr. Reed is rather less equilateral than the typical form. The 

 species itself is difficult of distinction from the young of T. pubescens. 



I also possess a perfect specimen of this shell from the Lower Glacial sand ofBelaugh. 



Thracia ventricosa, Phil. 2nd Sup., Tab. V, fig. 3; Crag Moll., vol. ii, p. 262, 



Tab. XXVI, fig. 5 ; 1st Sup., p. 156. 



Locality. Cor. Crag, Ramsholt. 



In the list of the Crag shells appended to Mr. Prestwich's paper, p. 141, 

 the one I called by the above name is said to be Thracia convexa, W. Wood, and I have 

 in consequence figured a specimen obtained by myself from the Cor. Crag of Ramsholt. 

 I thought, and still think, that the differences between the Crag shell and T. convexa 

 are sufficient for their being kept distinct, and the specimen now figured exhibits these 

 differences better than that figured in my original work; they consist in ventricosa 

 having a far greater length of the posterior part of the shell and a less tumidity of the 

 anterior. Indeed, the form of ventricosa is nearer to that of pubescens than it is to 

 convexa. 



In this, as in many other similar cases of living species approaching the Crag form, 

 T. convexa may be the descendant of T. ventricosa, but if so the time which has elapsed 

 since the deposit of the Coralline Crag has been sufficient to produce those differences, 

 which, as I have pointed out in the concluding remarks of my first Supplement (p. 192), 

 I consider should justify us in designating species as distinct. 



Pholas intermedia, S. Wood. 2nd Sup., Tab. VI, fig. 7 ; Tab. V, fig. 2 a — c. 



Dimensions. Length, 2 inches. Breadth of valve, 1 ^ inch. 



Localities. Cor. Crag, Gedgrave; Red Crag, Waldringfi eld. 



The specimen represented in Tab. V, fig. 2, is in the collection of Mr. Canham, now 

 in the Ipswich Museum, and was obtained from the phosphatic nodule pits at Waldring- 

 field. As the valves are held together by the Red Crag material within them, 

 I infer that the specimen died in the Red Crag, the material of which occupied the cavity 



