THE CAMBRIDGE GAULT AND GREEtfSAND. 293 



it best to figure some well-marked casts. The two chief features of 

 the Cambridge specimens are the well-defined spiral lines, four or five 

 on a whorl, and the occasional varices marking the position of former 

 mouths ; while Pictet and Roux describe the cast as smooth, though 

 they speak of the shell as cancellated. A comparison with the foreign 

 forms only will decide the question ; and this I have not yet been able 

 to make. 



Solarium Sedgwicrti, Seeley. 



! Solarium Sedgwidcii, Seeley, Ann. & Mag. Nat. Hist. 1861, vol. vii. 



pi. xi. f. 10. 



The Solaria of the Gault present great difficulties in their deter- 

 mination, so much so that Mr. Price and Mr. Newton, of Jermyn 

 Street, who have paid some attention to the subject, are inclined to 

 believe that all those of the " ornatum " type pass into one another. 

 The margin of S. clentatum is sometimes produced into spines ; and 

 sometimes the dentations are hardly visible, thus passing into S. 

 Hochatianum or S. ornatum ; the ornamentation of the shell also is 

 just as variable. S. Sedgwichii seems to present another link ; for 

 Mr. Seeley describes it as having " the inflated form of S. cirroide 

 and the angular margin of S. dentatum." 



M. Renevier can see little difference between S. cirroide and S. 

 HoeJiatianum (' Faune de Cheville,' p. 133) ; and certainly the latter, 

 as figured by MM. Pictet and Roux (' Gres Verts,' pi. 20), only ap- 

 pears to be a small variety of the former. 



I am therefore strongly disposed to coincide in the above-men- 

 tioned view, and to regard all these so-called species as only varietal 

 forms of one species, to which the* original name of " ornatum '* 

 might well be applied. 



Pleurotomaria Gibbsii, Sow. 



Pleurotomaria Gibbsii, Pict. & Camp. Ste.-Croix, ii. p. 441. 



Pleurotomaria gurgitis, D'Orb. Pal. Pr. ii. pi. 192. f. 4-6 ; Pict. 

 & Poux, Gres Yerts, p. 237, pi. 23. f. 2. 



The cast of this species has the umbilical face rather inflated, and 

 the whorls flat or slightly convex. 



Mr. Price finds it at Polkestone, both in Upper and Lower Gault ; 

 but no one has noted its occurrence at Cambridge except M. 

 Eenevier, in his ' Faune de Cheville,* p. 137, who also records the 

 three following species from the same locality. 



Pleurotomaria vraconnensis, Pict. & Camp. 



Pleurotomaria vraconnensis, Pict. & Camp. Ste.-Croix, ii. p. 443, 

 pi. 81. f. 3. 



These casts are of rather large size, with a flat umbilical face, 

 producing a well-marked keel ; the sinus-band leaves a distinct 

 spiral rib on the middle of the whorls. I think this is the shell 

 which Mr. Seeley entered as P. neocomiensis in the list appended to 

 one of his papers in Ann. & Mag. Nat. Hist. 1861 ; the two species 

 have many features in common. 



i2 



