88 INFERIOR OOLITE AMMONITES. 



From Ps. compactile they are separated by having rather thicker, more convex 

 whorls, and a plain, sloping, indistinct ventral area, instead of a very narrow flattened 

 depression ; and instead of a subconcave inner area with its inner marginal ridge 

 making a deeper umbilicus, they have a depressed inner lateral area causing the 

 umbilicus to be shallow. The two specimens which are figured (Plate XX, figs. 

 7, 8, and 9, 10) differ from each other considerably in the size and form of the 

 umbilicus. Fig. 9, moreover, is somewhat less compressed towards the inner area. 

 In reality these specimens appear to be forms partly intermediate between Ps. com- 

 pactile and the true Ps. Beyrichi, but are more easily separable from the former, 

 which is just what we should expect from their position. 



This species occurs in the Opalinum-zone. I have obtained it at Haresfield 

 Hill in Bed No. 15 (page 43), at North Nibley in Bed 6 (page 46), and at Coaley 

 Wood ; but it is certainly scarce, and seems to be of rather small size. Schloen- 

 bach quotes it from various places in Brunswick and Hanover, from the zone of 

 Trigonia navis. His figured specimens are much larger than any of mine. 



Plate XX, figs. 7 and 8, illustrate a specimen from Coaley Wood. It has only 

 the beginning of the body-chamber present. Figs. 9 and 10 show another specimen 

 from North Nibley. It has a larger, more excavated umbilicus than fig. 7 ; and 

 the umbilicus shows some small ribs. In the above figures the letter a marks the 

 carina when entire, the letter b the rounded ventral area without the test. 



Hildoceratim; [continued). 

 Genus — Hyperlioceras, 1 S. Buclcman. 



{Type — Hypebliocebas discites, Waagen sp.) 



Definition. — Discoidal, much compressed, strongly carinate, and involute, 

 except when, in adult age, the body-chamber is present. Whorls, with their sides 

 generally more or less parallel. Ribs, in youth, nearly straight, then projected 

 more and more on the lateral and ventral areas, and finally forming subfalciform 

 radii, which very seldom bifurcate. The ribs disappear at an early age, and then 

 the very smooth appearance is assumed, the whorls being ornamented only with 

 very fine sigmoidal lines of growth, projected forwards considerably on the lateral 

 and ventral areas, forming strong curves upon the test. The ventral area is 

 narrow and flat ; it carries a large, prominent, solid carina with a rounded outer 

 edge, and the carina occupies about one third of the ventral area. Even when the 

 test is absent the core is strongly carinate, while the siphuncle lies inside the 

 carina (Plate A, fig. 27). The inner margin is concave, but varies in its slope, the 



1 From 'vnep, Xt'ioi, Kepas, very smooth horn. 



