AEGOCERAS BECHEI. 381 



tubercles united by short bifurcated ribs ; from the outer row of tubercles bifurcate 

 and trifurcate ribs proceed across the siphonal area. Passing over the sides and across 

 the area many single ribs ascend between the tubercles. Siphonal area rotund and 

 highly convex, beautifully sculptured with longitudinal striae and transverse ribs ; aperture 

 widely expanded, a little flattened on the sides, and very convex externally. 



Dimensions. — Transverse diameter, 120 millimetres ; width of umbilicus, 10 milli- 

 metres ; height of aperture, 70 millimetres ; width of aperture, 70 millimetres ; the 

 smaller specimen has the same relative proportions. 



Description. — This fine Ammonite has a very globose shell and greatly enlarged 

 outer whorl ; the sides between the two rows of tubercles are slightly flattened ; the small 

 ribs below are nearly straight, about two to each tubercle, with one between the 

 tubercles ; the umbilicus is deep and narrow, so that the spire is nearly entirely 

 concealed. The longitudinal striae are sharply defined and limited to the structure of 

 the shell, being absent from the mould. 



The siphonal area is rotund and very convex, from each tubercle of the marginal 

 row, a bifurcate, and then a trifurcate, rib proceeds transversely across the area, with one 

 or two single ribs between the bifurcations, these form a very regular series of transverse 

 ribs with corresponding concavities between, the whole being intersected by numerous 

 close-set, longitudinal striae, which are extremely well defined in this species, and 

 produce a highly ornate surface on the extremely convex siphonal area of its beautiful 

 shell. 



The aperture is as wide as it is high, and occupies more than half the diameter of 

 the shell ; it has a rounded figure, slightly flattened on the sides, corresponding with the 

 depressed space between the lateral rows of tubercles. The lobe-line is extremely 

 complicated and much resembles the lobe-line of Aeg. striatum. The siphonal lobe 

 (fig. 5) is much shorter and narrower than the principal lateral, and ornamented on 

 each side with three branches, of which the terminal one is bifurcate. The siphonal 

 saddle is smaller than the princij)al lateral lobe, and terminates externally in three 

 ramified foliations, and internally in one. The principal lateral lobe is large, formed 

 of two branches on each side, and a long central branch with a bifurcate terminal 

 digitation. The lateral saddle terminates in three foliations on each side. The lateral 

 lobe has two external branches and one terminal digitation. The auxiliary saddle has 

 three foliations. The auxiliary lobes, four in number, are all small and oblique, and 

 gradually decrease in size from without inwards. 



Affinities and Differences. — This species undoubtedly resembles Aeg. striatum., and 

 by many continental authors is considered to be identical with it. Still I am satisfied the 

 following difierences are sufficiently permanent to justify their separation. In Aeg. 

 Bechei the whorls are much more involute, and the umbilicus narrower and deeper 

 than in Aeg. striatum. The tubercles, likewise, are smaller, the ribs much more slender, 

 and the longitudinal striae sharper and better defined than in the latter species. Herr 



