478 THE LIAS AMMONITES. 



whorls arc subquadrate, wider than high, and slightly involute, they are transversely 

 ornamented with 36 to 42 small costse which commence at the spiral suture and 

 cover the sides, some remain single, whilst others unite in pairs and form a tubercle 

 which develops a long outward directed spine ; the tubercles and spines occupy the 

 margin of the inner whorls and form a deep spiny umbilicus. On the outer whorl the 

 tubercles begin to disappear, and the costation then consists of a simple bifurcate 

 rib which sends its branches across the area. The siphonal area which is broad 

 and flat, is closely adorned with small costse derived from the fasciated tubercles, as 

 well as from the intermediate simple ribs that pass freely and singly up the sides and 

 over the area. The spire is formed of subquadrate whorls compressed in contact with 

 each other and marked by the elongated spines that proceed from the tubercles along the 

 line of the spiral suture. The aperture in section is subquadrate, and when the 

 termination is preserved it is found to consist of a circular contraction and a round 

 thickened band similar to the appendage I have figured as appertaining to Steph. commune 

 in PL LXXXIII, fig. 3. The septa are symmetrical on each side, the principal lateral 

 lobe is large and terminates in three large branches ; the lateral saddle is narrower than 

 the principal lobe and terminates in two large folioles of which the internal is the 

 largest. The inner lateral lobe has an irregular figure terminating in two horn-like 

 points. 



Affinities and Differences. — I have figured two types of this Ammonite, the large 

 tumid specimen (PL LXXXV, figs. 2, 3) from the Upper Lias of Chipping Warden, 

 Northamptonshire. The specimen (PL LXXXV, fig. 1) with large knobs and fasciated 

 costse resembles a variety of Stephanoceras fibulatum from the Upper Lias at Whitby. 

 This last specimen is not a satisfactory example, still it is the best I could obtain of 

 the species at Whitby. 



Stephanoceras Raqtjimanum, d'Orbigny. PL LXXXVI, figs. 5, 6, 7. PL LXXXVII, 



figs. 1, 2, 3, 4, 7, 8. 



Ammonites Requinianus, d'Orbigny. Paleont. Fr., Terr. Jurass., p. 332, pi. 106, 



1842. 



— — Ckapuis et Dewalque. Mem. Cour. Acad. Roy. Belgique, 



t. xxv, Foss. du Luxembourg, pi. vii, fig. 1, 1854. 



— — Q.uenstedt. Der Jura, p. 251, 1858. 



Diagnosis. — Shell discoidal; whorls tumid, one half involute, transversely cos- 

 tated ; sides inflated, covered with short, straight ribs, twenty to thirty, commencing 

 at the umbilicus, and half way up the side becoming tuberculated, fasciated, and 



