288 A. J. JTTKES-BROWNE ON THE RELATIONS OF 



termediate between S. Meriani and those first described with nearly 

 simple ribs, which might receive the varietal name of simplex. 

 They are easily distinguished from 8. cequcdis, Sow., by the convo- 

 lute portion being so closely coiled as not to produce an umbilicus, 

 as well as its much greater width across the back. In S. cequalis, 

 moreover, the side ornamentation takes the form of greatly thick- 

 ened ribs, instead of small tubercles. 



Anisoceras, Pictet. 



This genus was founded by M. Pictet in his ' Traite de Paleonto- 

 logie,' torn. ii. p. 705, to include fossils resembling Ancyloceras in 

 general form, but having the convolute portion twisted into an irre- 

 gular spire, instead of lying in one plane. The genus does not seem 

 to have been accepted in England ; but I think it is certainly re- 

 quired, though the species it comprises cannot all be determined 

 until the irregular AmmonitidaB of the Gault and Greensand are 

 more thoroughly known. Anisoceras, in the character and ornamen- 

 tation of its shell, is similar to Hamites, with which its species have 

 chiefly been confounded. 



Anisoceras armatus, Sow. 



Hamites armatus, Sow. Min. Conch, pi. 168. 



Anisoceras armatus, Pictet & Camp. Ste.-Croix, p. 62, pi. xlviii. 

 f. 1-6. 



Anisoceras perarmatus, Pict. & Camp. Ste.-Croix, p. 65, pi. xlviii. 

 f. 7, 8, and pi. xlix. 



Large fragments of this shell are not uncommon on the Cambridge 

 heaps, and appear chiefly to belong to the typical form, though some 

 specimens agree with the figures of A. perarmatus. I cannot re- 

 gard this latter form as any thing but a variety of A. armatus, from 

 which it only differs in the width between the tubercles, the straight- 

 ness of the ribs, and the smaller number of intermediate ribs ; more- 

 over, MM. Pictet and Campiche themselves figure a specimen which 

 they regard as forming a transition (pi. xlix. f. 7). 



Anisoceras Satjssureanus, Pict. 



Anisoceras Saussureanus, Pict. Ste.-Croix, ii. p. 67, pi. 1. f. 1-3. 



Hamites Saussureanus, Pict. Gres Yerts, p. 118, pi. 13. f. 1-7. 



Hamites Raulinianus, Oost. Ceph. Alp. Suiss. v. p. 75 (non D'Orb.). 



This species, so common at Cheville and Ste.-Croix, is not of such 

 frequent occurrence at Cambridge, where, however, it is far from 

 rare. 



In this species the tubercles do not appear like buckles tying two 

 ribs together as in A. armatus, but as simple rounded knobs on the 

 larger ribs ; these are also placed further apart and separated by 

 numerous intermediate ribs, making a very different ornamentation. 

 There are several other species of Anisoceras or Hamites among the 

 Cambridge collections which await determination, or are possibly 

 new species. 



