362 THE LIAS AMMONITES. 



specific name hrevispina. The type specimen was collected by the late Sir Roderick 

 Murchison from the Middle-Lias Shales at Pabba ; and I have had another specimen sent 

 me by Professor Geikie, P.R.S., for determination, collected by him from the Middle 

 Lias Pabba. 



The specimen figured in Plate L, figs. 13 and 14, was collected by the Rev. .1. E. 

 Cross, E.G.S., from the Ae^. Jamesoni-heds of Robin Hood's Bay. In this specimen the 

 sides of the whorls are much flattened, and each small, oblique, forward- directed rib 

 carries two small tubercles; the spire is so slightly involute that both tubercles are 

 visible on the sides in all the six turns of the spire. The siphonal area of this specimen, 

 shown in fig. 14, exhibits a convex surface crossed at intervals by the ribs which stretch 

 transversely from one tubercle to the other. The intermediate concave valleys are 

 smooth and without ornament. The lobe-line is very complicated (PI. XXXII, fig. 4). 

 The siphonal lobe is shorter and wider than the principal lateral, and ornamented on 

 each side with four branches, each many-digitate. The siphonal saddle is as large as the 

 principal lateral lobe and divided into two equal foliations by a projecting process. 

 The principal lateral lobe has a very irregular figure provided with three large ramified 

 terminal branches and several small upper ones. The lateral saddle smaller than the 

 siphonal is divided into two unequal foliations, of which the internal is the larger. 

 The lateral lobe and the auxiliary lobes are small and very oblique, the whole forming 

 a highly complicated structure. 



Ajjiniiies and Differences. — This species resembles Aegoceras Valdani and Aeg. 

 Birchii in having two rows of spines upon the lateral ribs of its shell. It difiers, 

 however, from Aeg. Valdani in possessing a round siphonal area, crossed by folds and 

 depressions, and a more simple lobe-line ; and from Aeg. Birchii in having flatter ribs, 

 smaller tubercles, a narrower siphonal area and wider folds thereon, and in possessing a 

 much less complicated style of lobe-line. 



Locality and Stratigraphical Position. — It occurs in the Middle Lias of Pabba in the 

 Jamesoni-zone, likewise in the same horizon at Robin Hood's Bay, Huntcliff", and 

 Normanby, Yorkshire. The specimens figured PI. L, figs. 13, 14, came from Robin 

 Hood's Bay. 



Foreign Distribution. — In France it is found at Saint-Christophe, Saone-et-Loire ; 

 Saint-Amand, Cher. In North Germany it is the associate of Aegoceras Jamesoni in all 

 the localities that I have noted for that Ammonite. In South Germany it occurs at 

 Gammelshausen, Hechingen, and Balingen. 



