46 



FAUNA OF THE CORNBRASH. 



even resembles that called Gad, tchefldni in the Callovian of Russia (D'Orbigny, 

 * Geol. Russia,' pi. xxxv, figs. 14, 15). 



Distribution, — The specimens are from Garsdon (2), Bedford (3), Castor (3), 

 Roxholme (1), and from an unknown locality (1). 



Sub-species Macrocephalites herveyi Sowerby. Plate III, fig. 7; Plate IV, fig. 2. 



1818. Ammonites herveyi Sowerby, Mill. Conch., vol. ii, p. 215, pi. cxcv. 



Types. — There are two co-types, both of which are now in the British Museum 

 (Nos. 43883 and 46485). Of these the author notes that the border of the 

 umbilicus is angular and its sides are vertical, the ribs bifurcate or trifurcate and 



*&% 







f^ltn 



?: 



<~ 

 x 



if 



Fig. 4. — Adult suture-line of Macrocephalites compressus. 



do not match as to their union on the opposite sides. They enlarge gradually, 

 and the thickness is half the height. The numerical characters are given in 

 Nos. 16 and o(J of Table I (p. 40). One of them is said to have come from 

 Bradford-upon-Avon, and the other from the drift. 



Description. — The above description would suit so nearly J\I. macro cephalus s.s. 

 that it is no wonder that M. herveyi and this have been merged by authors, and that 

 the former can only be regarded as a sub-species of the latter. Nevertheless, there 

 seem to be in most cases several distinctions between them. (1) M. herveyi has a 

 less relative thickness; it is seen from Table I that in M. macrocephalus it is always 

 greater than "70 of the diameter, but in M. herveyi it is always less. (2) On the inner 

 half the whorls are flatter and descend suddenly into a nearly vertical umbilicus, 

 instead of bending round gradually into it. (3) The additional ribs which are found 

 near the periphery rise gradually from points at some distance from the umbilical 

 edge and are not simple bifurcations. And (4), most characteristically, the ribs of 

 M. herveyi have a sigmoid curvature, with the concavity forward near the 

 umbilicus. 



