316 MOLLUSCA. 



The ScAPHiTEs, Sowerb., are those in which the whorls are con- 

 tiguous and in the same plane, the last one excepted, which is de- 

 tached and reflexed on itself(l). 



Some, Baculites, Lam., are entirely straight without any spiral 

 portion whatever. 



Some of them are round(2), and others compressed(3). The last 

 "Sometimes have a lateral siphon. 



The first cells of some of them the Hamites, Sowerb., are arcu- 

 ated. 



Finally, those which vary most from the usual form of this family 

 are the Turrilites, Montf., 1 18, where the whorls, so far from run- 

 ning in the same plane, suddenly descend, giving to the shell that 

 form of an obelisk which is called turreted(4). 



It is also thought, and from similar considerations, that we should 

 refer to the Cephalopoda, and consider as internal shells the 



Camerines, Bmg. Nummulites, Lam. 



Commonly called Nummulites, lenticular stones, See. which are 

 only found among fossils, and present, externally, a lenticular figure 

 without any apparent opening, and a spiral cavity internally, di- 

 vided by septa into numerous small chambers, but without a siphon. 

 They constitute the most universally diffused of all fossils, forming, 

 per se, entire chains of calcareous hills and immense bodies of build- 

 ing stone(5). 



The most common, and those which attain the greatest size, form 

 a complete disk, and have only a single range of cells in each 

 whorl(6). 



(1) Sc. obliqiius, Sowerb.; Cuv., Oss. Foss., II, part II, pi. li, f. 13. 



(2) Baculites vertebralis, Montf, 342; Fauj., Mont, de St Pierre, pi. xx'i. 



(3) The Tiranite, Montf., 346; Walch., Petrif, Supp., pi. sii, constitutes the 

 genus Rhabdites of Haan, who refers the Icthtosahcoxites of Desmar. to it. 



(4) Montf Journ.de Phys., an VII, pi. i, f 1. There are some doubts as to the 

 position of the siphon. Perhaps, as M. Audouin observes, what has been .taken 

 for It, is the columellar convolution. 



(5) The stone termed picrre de Laon is wholly formed of Nummulites. The 

 pyramids of Egypt are placed upon rocks of this description, which also furnished 

 the materials of the superstructure. See the Memoir of Fortis on the DiscoUtes 

 in his work on Italy, and that of M. Hericart de Thury, as well as Lam., Anim. sans 

 Verteb., VIII, and M. D'Orbigny, Tab. Method, des Cephalopodes. 



(6) Nautilus mammilla, Ficht., and Moll., VI, a, b, c, d^Naut. knticularis, 

 VI, e, f, g, h, VII, a h. To this genus also we refer the Licophee and Egeone, 

 Montf, 158, 166, and his Rotalitk, 162, which differs from the Rotalies of La- 

 marck. 



