27 



CaliJtbriiiaii shell ai)plies with ;j;reat exactness to the present specimens, 

 except in one particular. Each rib in the type of .4. Stoliczkanus is de- 

 scribed as bearing six tubercles, three on eacli side of the periphery, but 

 there are usual!}' ncarlv double that number in the corresponding costai 

 of the fossils collected b}- Mr. Kichardson. Although this might appear 

 to be an important dittercnce, it is doulitful whether it is of more than 

 varietal value. The number of tubercles to each rib is variable in actual 

 specimens, and they show a marked tendency to divide into two or three 

 in the course of growth. Thus, in the last whorl but one of the original 

 of Plate IV., tig. 1, there is a single tubercle on the umbilical margin, 

 another on the middle of the sides, and a third triiid one on th'e edge of 

 the peripher}'. The description of the tuberculation of the type agrees 

 so well with some of the Queen Charlotte Island specimens, that the 

 latter are, (for the present at least) regarded as simpl}' a variety of 

 A. Stoliczkanus with rather more numerous tubercles than usual, to 

 each rib. 



Pictet's gi-oupMammillati, in which this species is placed, differs from 

 the Eotomagenses chietiy in the absence of tubercles or carination on the 

 peripher}^ of the shell. It is partly made up of Ammonites taken from 

 that division and from the Dentati, ^4. laticlavius of Sharpe, from the 

 Grey Chalk of the Isle of Wight, bears a considerable resemblance to 

 this shell, but the whorls of the English fossil are flatter, and its aperture 

 is much higher than wide. 



Group III. — Macroccphali, Von Buck. 



Subgenus Stephanocek.\s, WAAiiEN (Paes. ) — " Geognostich Pahtoiitologische Bei- 

 trage," von Dr. E. W. Benecke, Mimchen, 1869. Vol. II., page 248. 



Ammonites Loganianus. (N. Sp.) 

 Type. Plate VIII., fig 2. 



Shell compressed, but rather thick ; inner whorls entirely covered, 

 except about three-fourths of the last one;* umbilicus of medium 

 size. 



The early volutions are a])parently ver}- strongly involute, but the 

 two outer ones are much more loosely coiled. The last whorl is 

 obliquel}' compressed at the sides, which are widest just before they 



* 111 the only two specimens obtained, the centre was covered by the matrix and it is just possible 

 tluit if this were removed, rather more than one volution and three-fourths of another would be visible 

 externally. Still, the shale was detached from the innbilicus of the examjile figured, to a de]>th of nearly 

 three-quarters of an inch, without a trace of the inner whorls being exposed. 



