374 THE LIAS AMMONITES. 



with age develops spines ; this Jpg. Carusense never does. It is altogether a unique 

 Ammonite from the basement bed of the Middle Lias. 



Locality and Stratipraphical Position. — I have found this species in the Aeg. Jamesoni 

 beds, Swindon Road, near Cheltenham. 



Aegoceras Slatteri, Wright, nov. sp. PI. L, figs. 1 — 8. 



Diagnosis. — Shell discoidal, depressed ; whorls high, two thirds involute ; sides 

 ornamented with thick, obtuse, curved ribs, which alternate with concavities of the 

 opposite side; siphonal area convex and smooth, the knobs of the ribs alternating on the 

 margin ; aperture oblong, narrow. 



Dimensions. — Transverse diameter 55 millimetres; width of the umbilicus 15 

 millimetres ; height of aperture 23 millimetres; transverse diameter 13 millimetres. 



Description. — This singular Ammonite was collected by my friend Mr. T. J. Slatter, 

 E.G.S., of Evesham, from the Lias of Broughton, near Pershore. The specimens are 

 all fragmentary, and therefore I describe it with some hesitation; the shell is discoidal 

 and much compressed ; the whorls high and quite one half involute (fig. 1) ; the 

 sides ornamented with bent, obtuse, recurved ribs, which thicken out into knobs 

 at the margin of the siphonal area; the ribs on the right side of the shell correspond 

 to concavities on the left, so that the costse on the right and left sides alternate with 

 each other, which becomes very obvious when we examine the specimens (figs. 2, 4, 5). 

 In early life the shell appears to have resembled an Amaltheus, and had a small carina 

 in the centre of the area (figs. 6, 7), which carina appears to be covered over by the 

 future whorl as in fig. 3, and to be indicated in fig. 4. The thin shell is only partially 

 retained on a portion of some of the fragments. In the larger segments the siphonal 

 area is rounded and marked by transverse lines, and the terminal knobs of the ribs 

 form conspicuous objects in the specimen delineated in fig. 5. 



The lobe-line (fig. 8) is very simple. The siphonal lobe is about the size of the 

 principal lateral with three lateral digitations on each side, and a single terminal point. 

 The siphonal saddle is wide and deep and terminates in three principal foliations. The 

 principal lateral lobe is nearly as long and a little wider than the siphonal, and has three 

 lateral digitations on each side, with a bifid termination. The lateral saddle in size and 

 structure very much resembles the siphonal, and has four terminal folioles around its 

 termination. The lateral lobe is smaller than the principal lateral, the outer margin is 

 serrated, and its terminal portion bushy. The auxiliary lobe is very small and simple. 



Affinities and Differences. — The style of the ribs in this species has no parallel among the 

 Lias Ammonites ; at first I thought it might be an accidental monstrosity or an acquired 

 alternate character of ribbing fronj descent, as all the specimens hitherto found possess the 



