156 GUIDE TO THE FOSSIL INVEETEBEATE ANIMALS. 



Gallery Spirulirostra the apex of the chambered shell is coiled quite 

 'able c ^'o^iiid, and a part of the sheath has come to lie above it ; the 

 l" rest of the sheath is greatly reduced and ends in a sharp 

 point. By further coiling of the shell, by reduction of the 

 pro-ostracum, and by the final disappearance of the guard, 

 was produced the coiled shell of Spirtda (Fig. 85 c). This is 

 very like a shell of the earlier coiled Ammonoidea, but the 

 siphuncle is on the inner side of the coil, the septal necks 



a h 



Fig. 86, — Cephalopods with thin enclosed shell. a, Belemnoteuthis 

 antiqua, Oxford clay, Wiltshire; showing phragmocone {ph), ink- 

 sack (i), folds of mantle (w), one of the eyes (o), and the short arms {a) 

 with their hooks (h) ; one-third natural size, b, Dorateuthis syriaca, 

 Cretaceous, Lebanon ; showing shell and ink-sack as i though the 

 enclosing mantle were transparent ; nat. size. 



pass backwards, and the shell is very thin. It is almost 

 entirely enclosed by the mantle. 



I ' Meanwhile a distinct line of evolution was progressing. 

 Among the beautifully preserved fossils of the Oxford Clay 

 of Christian Malford is the specimen of Belemnoteuthis 

 antiqua described by G. A. Mantell (Fig. 86 a). Here are to 

 be seen 10 short hook-bearing arms, the head with its well- 

 developed eyes, the folds of the mantle, the fins, the ink-bag. 



