450 SUPPLEMENT. 



i: 



Gyroceras, D'Orb. (not Meyer) has been employed for the principal 

 fossils included in Ci/rtoceras by Goldfuss. The name was originally given 

 by Meyer, to G. (jraciJis, Bronn {Spirula, Goldf. IMS. 1832, Litnites, 

 Quenstedt) which is the Goniatites compress7is of D'Arch. and Vern. I 



Trigonocerc.s (paradoxiciun) Mc Coy, is a form of Nautiloceras, D'Orb. 

 (Cyrt. Eegocerus, Miinst.) with a sub- spiral shell. ^ 



' Discites (iSIc Coy) is closely allied to the last, differing in the whirls 

 beino- compact. It may be doubted whether any of the Palgeozoic f 

 " Nautilidae" really belong to that family. j 



Ascoceras. — This curious fossil (which has been recently found at !. 

 I.udlow, by Mr. Salter) only resembles Ftrjchocems in appearance. It is j 

 slishtlv curved, and has a dorsal siphuncle, but the septa are bent and pro- 1 

 longed forwards on the ventral side to such an extent as to give an appearance i 

 of the whole shell being doubled up. 



Ammonites Jason, Reinecke (A. Gulielmi, Sby). The fossil figured, 

 PI, III 5. is A. spinusns, Sby. (=A. ornatus, Schl.) and is certainly distinct 

 from the finely ribbed species which occurs with it, and to which the name 

 Jason should be restricted. 



CLASS II. GASTEROPODA. 



Classification hy lingnal dentition. 

 The researches of Dr. Loven have been followed by many observations on 

 genera not figured in his admirable memoir,* and by attempts to remodel the 

 arrangement of the Gasteropoda by the aid of peculiarities in their dentition. | 

 Whatever improvements may be thus obtained, it does not appear desirable to \ 

 introduce a new terminology for divisions long since well established, and I 

 already over-burdened with classical names.f J 



The patterns, or types of lingual dentition, are on the whole remarkably .j 

 constant ; but their systematic value is not uniform. It must be remembered ] 

 that the teeth are essentially epithelian cells, and like other superficial organs ,.j 

 liable to be modified in accordance with the wants and habits of the creatures. 

 The instruments with which animals obtain their food are of all others most • 

 subject to these adaptive modifications, and can never form the basis of a ^1 

 philosophical system.:}: ,'l 



* Ofversigt af Kongl. Vetensk. Akad. Fbrhandl. 1847. J 



+ The following names were proposed by Troschel (in Wiegman's Handbuch der • 

 Zoologie, 1848) and Gray (An. Nat. Hist.) for the principal types of lingual dentition. ], 



a. Taenioglossa, teeth 3. 1. 3 : Litorina, Natica, Triton, t| 



b. Toxoglossa, teeth 1. 0. 1 ; Conus, Terebra.' 



c. Hamiglossa, teeth 1. 1. 1: Murex, Buccinum. 



d. Rachiglossa. teeth ('. 1. 0; Voluta. Mitra? 



e. Gymnoglossa, teeth ; Pyramidelia, Cancellaria, Solarium ? 

 /. Rhipidoglossa, teeth 00. 1. 00 ; Nerita, Trochus. 

 X The carnivorous opossums have teeth adapted for eating flesh, but are not on that 



account to be classified with the placental carnivora. 



