THE CAMBRIDGE GAULT AND GREENSAND, 299 



Inoceramtts concentricus, Park. 



Inoceramus concentricus, D'Orb. Pal. Fr. p. 506, pi. 404; Pict. 

 & Roux, Gres Yerts, pi. 42. f. 2. 



Three specimens of what is probably a large variety of this shell 

 are preserved in the "Woodwardian Museum ; and others are in the 

 possession of Mr. J. Carter, M.R.C.S., and of Mr. A. F. Buxton, 

 Trinity College. The rarity of this species at Cambridge must, I 

 suppose, be accounted for in the same way as that of its congener, 

 J. sulcatus. It is not to my knowledge found in the Upper Gault of 

 Bucks. 



Arca Hugardiana, D'Orb. 



Area Hugardiana, Pal. Fr. p. 216, pi. 313. f. 4-6 ; Pict. & Roux, 

 Gres Yerts, p. 457, pi. 36. f. 1 ; Pict. & Camp. Ste.-Croix, iii. p. 560. 



The shells or, rather, casts which I regard as belonging to this 

 species, have been considered by Mr. Seeley to be a " dwarf race" of 

 Arca irregularis, D'Orb. ; but a careful comparison of those in the 

 "Woodwardian Museum has led me to differ from this identification 

 and to refer them to Arca Hugardiana, D'Orb. In this con- 

 clusion Mr. Price fully agrees with me, and considers that the little 

 Arca which is not uncommon in the Upper Gault of Folkestone 

 belongs to the same species. 



NVCTTLA BIVIRGATA, SOW. PL XY. f. 4-8. 



Nucula bivirgata, Sow. Geol. Trans, ser. 2, vol. iv. pi. xi. f. 8 ; 

 D'Orb. Pal. Fr. pi. 303. f. 1-7. 



Among the species of Nucula which have been found in the 

 Cambridge nodule-bed, one is by far the commonest, and has been 

 identified by Mr. Seeley with N. simplex, Desh., a Neocomian spe- 

 cies. I regret that I must again differ from that gentleman, having 

 come to the conclusion that these well-marked casts are those of 

 N. bivirgata, a characteristic species of the Gault. I was for some 

 time uncertain to what species they belonged, but was rather 

 inclined to consider them young forms of N. pectinata, Sow. I 

 found also that MM. Pictet and Campiche (Ste.-Croix, iii. p. 414) 

 give the " Gres vert de Cambridge (?)" as a locality for that fossil. 

 On consulting Mr. Price about them he told me that similar casts 

 had often been found in the Folkestone Gault, but that he was not 

 certain about their identification. He very kindly allowed me, 

 however, to take specimens of both N. jpectinata and N. bivirgata 

 out of his collection, and to remove their shells, in order to compare 

 the casts with the Cambridge forms. The result was that the cast 

 of N. bivirgata proved to be of the same shape and proportions ; and 

 we were satisfied that the doubtful forms belonged to that species. 

 The presence of a specimen in the Woodwardian Museum retaining 

 the phosphatized shell confirms this conclusion. 



I have since repeated the operation on other specimens from 

 Folkestone, and with the same satisfactory result, disclosing, more- 



