THE CEPHALOPODA. 



201 



and more or less straight in the interval. The bends 

 Septa transverse, divided regularly into six unequal lobes, 

 round or oval, with or without processes or oval bands. 



few and never in contact. 

 Siphuncle marginal. Mouth 

 All are Cretaceous forms, of 



which Hamites elegans, d'Orbigny (fig. 92), is a good type from the Gault. 



k. Species straight. 



Genus Baculites, Lamarck. Shell straight, conical, cylindrical or compressed, with 

 parietes articulated by sinuous sutures. Septa approximate, perforate, and much fringed 



Fiu. 93. — Baculites anceps, Lamarck. 



near the circumference. The last dwelling chamber is very large, and formed a long 

 sheath. Siphuncle marginal. These straight Ammonites are found from the Neoco- 

 mian formation to the Upper Cretaceous. Baculites anceps, Lamarck (fig. 93), is a 

 type. 



/. Species with shell spiral and turreted. 



Genus Turrilites, Lamarck. Shell spiral, turreted; whorls contiguous, and 

 exposed, with articulated walls formed by sinuous sutures (fig. 94). Spire dextral or 

 sinistral, umbilicated throughout. Septa transverse, divided into six lobes, foliated at 

 their margin. Mouth round. Siphuncle marginal, continuous. The Turrilites are true 

 Cretaceous forms. Some species from the Lias were referred by d'Orbigny to this genus. 

 These, however, have been proved to be only distorted species of Ammonites well known 

 in the beds in which they are found. Type, Turrilites catenutus, d'Orb. (fig. 94). 



Fig. 94. — Turrilites catenatus, d'Orb. Fig. 95. — Selicoceras Robertianum, d'Orb. Fig. 96. — Hetoroceras Emerici, d'Orb. 



