278 SCAPHITE. TURRILITE. 



borough. (See Phillips' Geology of Yorkshire.) Some of 

 the larger species equal a man's wrist in diameter.* 



Scaphite. 



The Scaphites constitute a genus of EUiptical chambered 

 shells, (see PI. 44, Fig. 15, 16,) of remarkable beauty, which 

 are almost peculiar to the chalk formation ; they are so 

 rolled up at each extremity, whilst their central part conti- 

 nues nearly in a horizontal plane, as to resemble the ancient 

 form of a boat ; whence the name of Scaphite has been ap- 

 plied to them.f 



It is remarkable that those approximations to the struc- 

 ture of Ammonites which are presented by Scaphites and 

 Hamites, should have appeared but very rarely, and this in 

 the lias and inferior oohte,J until the period of the cretaceous 

 formations, when the entire type of the ancient and long con- 

 tinued genus Ammonite was about to become extinct. 



Turrilite. 



The last genus I shall mention, allied to the family of Am- 

 monites, is composed of spiral shells, of another form, coiled 



* The Hamites grandls, (Soweiby, M. C. 593,) from tlie Greensand at 

 Hythe, is of these large dimensions. 



t The inner extremity of the Scapliite is coiled up like tliat of an Ammo- 

 nite, (Fl. 44, Fig. 15, c. and 16) in whorls embracing one another; the last 

 and outer chamber (a) is larger than all the rest together, and is sometimes 

 (probably in the adult state) folded back so as to touch the spire, and 

 thereby materially to contract the mouth, which is narrower than the last or 

 outer chamber. (Pi. 44, Fig. 15, b.) In this character of the external cham- 

 ber, the Scaphite differs from the Ammonite; in all other respects it es- 

 sentially agrees with it; its transverse plates being numerous, and pierced by 

 a marginal Siplumcle, at the back of the shell (Fig. 16, a.;) and their edges 

 being lobated, deeply cut, and foliated. (Fig. 15, c.) 



t The Scaphites bifurcatus occurs in the Lias of Wurtemburg, and Ha- 

 mites annulatus in the Inferior oolite of France. 



