Lamarck's Genera of Shells. 249 



ing the rest ; internal parietes articulated by sinuous sutures. 

 Septa transverse, lobed at the circumference, and perforated by a 

 marginal tube. 



Type. Orbulites subradiatus *. (Ammonites subradiatus. 

 Sowerby.) 

 Shell lenticular, umbilicattd, carinated and radiated; radii 

 twice curved, obscure, excepting near the margin, where they are 

 bifid ; umbilicus small ; keel entire ; aperture sagittate. 



From a mass of olite, found on the road between Bath and Bristol. 



PI. vi. Fig. 232. 



3. Ammonoceratitest. 



Shell corniform, arched, subsemicircular ; parietes articulated by 

 sinuous, ramose, indented sutures. Septa transverse, sinuous, 

 lobed and indented at the circumference. Tube or siphon mar- 

 ginal, not perforating the septa. 



The ammonoceratites seem to be to the multilocular shells with 

 indented septa, what the spirula is to those with simple septa. In 

 either case the whorls of the spire are not contiguous, and the 

 present genus appears not even to form one complete whorl. The 

 upper extremity is flattened at the sides, so as to become lingui- 

 form. 



Type. Ammonoceratites glossoidea%. 



Shell very large, thick, cylindrical, arched, rather flat at the 

 sides, inner side somewhat concave ; apex compressed, linguiform. 

 Said to be found in India. PI. vi. Fig. 233. 



* Subradiated. Our figure is from a specimen lent us by our kind friend 

 Mr. G. B. Sowerby, and which has been drawn and described in the 5th vol. 

 or the Mineral Conchology. Lamarck has described five species of orbnlite3, 

 but given no reference to any figure of either of them, except to a doubtful 

 one of the third, O. striata. We have adopted Mr. Sowerby's specific name and 

 description of the specimen we have figured, which does not belong to either 

 of the five species mentioned by Lamarck. 



t From Afj.fj.rn, ammon, and xEpa?, a horn. 



X From y\a><T<ra., a tongue, and ei&o?, form. Our figure is copied from that in 

 Bowdich'a Elements of Conchology, who calls it A. LamarcHi, and says, in a 

 note, " The locality is unknown. M. Lamarck purchased it by accident: he 

 kindly allowed me to take it home, in order that the figure, which is the first 

 that has been made, might be as accurate as possible." Part I. p. 21. 



