ANIMAL TO ITS SHELL IN SOME FOSSIL CEPHALOPODA. 99 



(PI. 20. figs. 5, 6, 7). It is a natural cast, and has the following dimensions : — Diameter 

 of shell 18'5 mm. ; width of umbilicus 7"5 mm. ; height of outer whorl G%j ; greatest 

 thickness 4 mm. At the base of the body-chamber the whorl is 5 '5 mm. high and 

 3'5 mm. thick. The shell is somewhat comjjressed, the inclusion very slight, and the 

 umbilicus wide and shallow. The body-chamber occupies rather more than one-quarter 

 of the last whorl, its inner (dorsal) edge subtending a chord of 8 mm. on one side and a 

 little less on the other side. Erom the fractured anterior end of the body-chamber a 

 double feebly-impressed line passes backward at a distance of 1 mm. from the suture 

 (tig. 6) ; then, diverging slightly, the two lines cross the whorl in a rather deep forwardly- 

 concave curve, their greatest distance from each other being rather more than 1 mm. 

 Approaching each other slightly, but without touching, they curve forward at the 

 periphery, each forming a submucronate jioint before passing on to the other side. It is 

 to be noted that these points are not in the median line of the periphery, but slightly 

 ou one side (fig. 7). The posterior of the two lines crosses the lateral area about 1 mm. 

 in advance of the anterior portion of the first lateral saddle. Ou the left side of the 

 anterior end of the body-chamber (fig. 5) the double line just described curves slightly 

 towards the periphery, but the opposite side, being a little shorter, does not exhibit this 

 curvature. This double line probiibly represents a j^oi'tion of the anterior boundary of 

 the shell-muscle, the two lines on the lateral and j^eripheral areas indicating the position 

 of the anterior and posterior boundaries resijectively of the annulus. 



CEcoTiiAUSTEs, Waagen. 



CEcotrmistes crenatus, Bruguiere, sp. — Two examples in the British Museum Collection 

 (No. 8968), from the Oxfordian of Doubs, France, exhibit what appears to be the 

 muscular im2)ressiou. Both are natural casts. 



One (PL 20. fig. 9) of these (No. 8968 b) has the following dimensions (exclusive of the 

 spines on the periphery) : — diameter 11 mm. : width of umbilicus 3 mm. ; height of 

 outer whorl 5 ram. ; thickness of ditto 3 mm. At the base of the body-chamber the 

 height of the whorl is 4 mm., and its thickness 2"5 mm. The septate part of the shell 

 and the extreme base of the body-chamber are of a reddish-brown colour, while the rest 

 of the body-chamber is of a much darker shade, a dark and very distinct line marking 

 the division near the base of the body-chamber. This line appears to be the anterior 

 border of the muscultir attachment of the animal. It commences from the suture only a 

 short distance in advance of the last septum, and crosses in a radial direction the inner 

 half of the lateral area until reaching the lateral saddle where it is 0*75 mm. in advance 

 of the suture-line ; it then curves slightly backward, making a very shallow curve, uatil 

 it reaches a point about 1'25 mm. from the median line of the periphery, where it turns 

 somewhat abruptly forward, and reaches the median line of the periphery, 2*25 mm. \\\ 

 advance of the summit of the outer (or peripheral) saddle, thus forming on the periphery 

 a subtriangular projection. A precisely similar line is seen on the opposite side of the 

 cast, but in tliis species there does not apjiear to be any forAvard prolongation near the 



