ANIMAL TO ITS SHELL IN SOME FOSSIL CEPHALOPODA. 101 



The smaller example (No. C. 51iO h), wliich exliibits the muscular attachment, has the 

 following dimensions (excluding both the height of the peripheral spines and the 

 inflated terminal portion of the body-chamber) : — diameter 15 mm. ; width of umbilicus 

 4 mm. ; height of outer whorl 6'5 ; thickness 1 mm., the whorl at the base of the body- 

 chamber being 4'5 mm. high and 3 mm. thick. In this specimen the outer boundary of 

 the forward ijrolongation of the muscular attachment is slightly more distinct than in 

 the example already described, and appears to be continued backward as a dark (not 

 incised) line into the second lateral lobe on one side of the specimen and on to the second 

 lateral saddle on the opposite side, but txt about 2'5 mm. from the last septum it gives 

 off a branch which curves outward towards the peripheiy, where it is bent slightly 

 forward. The width of the forward prolongation of the impression is 1"5 mm., the most 

 anterior part of the impression being 5 mm. from the last suture-line. 



The form and position of the muscular attachment in this species are also exhibited 

 by a specimen * (No. 22267) in the British Museum from the Brown Jura ^, Beuren, 

 Wiirtemberg ; it agrees with that already described in the example C. 5110 a. 



In this species, then, the shell-muscle seems to have been attached to the long flattened 

 siu'face on the inner area of the body-chamber. The anterior border of the shell-muscle 

 and of the annulus agrees almost precisely wdtli that described and figured by Oppel in 

 his well-known figures of Ammonites \z:=^Oppelia\ steraspis from the Lithographic Stone 

 of Solenhofen, Bavaria, a fact which supports Prof. Zittel's arrangement of the genera 

 Distlchocerus and Oppella in the same subfamily [OppdirKc). 



S T E p H A N o c E R A T I D ^, Ncuuiayr, emend. Zittel. 



Stephanoceras, Waagen. 



8tep}ianoceras BanJcsii, J. Sowerby, sp. — There are indications of the muscular attach- 

 ment of the animal in Sowerby's type-specimen, which forms part of the British Museum 

 Collection. It is a natural internal cast from the Inferior Oolite of the West of England, 

 but the 2^recise locality is not recorded. Its diameter is about 230 mm. (about 9 inches) 

 and its thickness about 150 mm. (or nearly six inches). One-third of the outer whorl is 

 occupied by the body-chamber, the base of which is 50 mm. high and 130 mm. mde. 

 The inner area of the whorl is convex and slopes considerably towards the umbilicus. 

 On the inner area, and arising from the suture of the shell at a point 43 mm. in advance 

 of the last sejjtum, there is a faint impressed line which jiasses backward and outward 

 across the inner area, crossing the umbilical mai'gin at about 30 mm. posterior to its 

 point of origin and 25 mm. from the suture of the shell. Arising from the suture of the 

 shell, and at a point 20 mm. posterior to the line cxlready described, there is another groove 

 which is rather more distinct and passes backward (more quickly than the anterior line) 

 and outward for rather more than 10 mm., then, with a forwardly-concave curve, passes 



* A peculiaritj- about this specimcu is that the chambers are arranged as it were in pairs, a large loculus being 

 succeeded by a small loculus. This is certainly the case with the last sixteen chambers. 



