GASTEROPODA. Ill 



Ammonites Braikenridgii, Sow. Plate XIV, fig. 1. 



Ammonites Triptolemus, Bean. MS. 

 ? — Braikenridgii, Sow. 1813. Min. Con., t. 184. 



— — D'Orb. Ter. Jurrass., t. 135, figs. 2, 3. 



A. Testa discoided, anfractibm (5 — 6) exjjositis, subrotundatis, costatis ; costis (30 — 36) 

 externe tuberculatis, in medio laterum bifidis, subinde trifidis, continuis ; dorso subconvexo ; 

 aperturd transversa, subdepressd, externe angidatd. 



A discoidal shell, with 5 — 6 exposed, somewhat rounded and costated volutions ; with 

 30 — 36 marginal costse, tuberculated externally, from each of which arise, about the 

 middle of the side, 2 and sometimes 3, rather obtuse smaller ribs, passing over the back ; 

 aperture wider than high, somewhat convex, with angular sides. 



This Ammonite (forwarded to us with the name, A. Triptolemus), belonging to the 

 section Coronarii, appears to be intermediate to A. Hiimphriesianus and A. Braikenridgii, 

 with the latter of which it is the more closely allied, but differing from it by the smaller 

 costae (in the cast) not being wholly enveloped by the later volutions. We regard the 

 specimen figured as only the adult state of this species. 



Locality. Near Scarborough. 



Class — Gasteropoda. 



Alaria Phillipsii, D' Orb. sp. Plate III, fig. 5; and Plate XV, figs. 15, 15«. 



? Rostellaria hamus, var. )3, Deslong champs. 1842. Mem. Soc. Linn, de Normandie, 



torn, vii, p. 174, t. 9, fig. 36. 



(See description, antea page 18.) 



We have provisionally retained (page 18) M. D'Orbigny's specific name for the 

 Yorkshire shell, believing that the one figured as Rostellaria composita, by Phillips, pre- 

 sented certain differences from that described in the ' Min. Conch.,' occurring in the 

 Oxford Clay of Weymouth. But Mr. Sowerby distinctly states that he has received the 

 same species from near Scarborough, so that the differences may prove, when a larger 

 number of specimens shall have been examined, to be due merely to variations arising 

 from local conditions. The Yorkshire shell appears to be identical with Rostellaria hamus, 

 var. |3, of M. Deslongchamps, cited above, from the Great Oolite of Ranville. 



Locality. Near Scarborough. This species is also found in the Inferior Oolite of 

 Yorkshire, and in the same formation at Dundry and Bridport. 



