254 CLASSIFJOATION. 



senting 94 species of cephalous moUusks. The first glance at 

 these plates suffices to show clearly that the lingual armature 

 confirms the most of the ancient divisions. Thus, the Cephalo- 

 pocls, Pteropods, Heteropods, Scutibranchs (in the sense of Quoy 

 and Gaimard, including the TrochidtB), are also distinguished 

 by the teeth. The conchological analogy between Pleurotoma 

 and Conus had already been shown by Sowerby. There existed, 

 nevertheless, certain anomalies until then inexplicable, on 

 account of the small number of observations made, as for 

 example, the analogy between Philine and Scaphander and the 

 Gymnobranchs. The want of teeth must not be considered as 

 fatal to the systematic value of characters found in these organs. 

 The teeth accepted as an exclusive -character have, doubtless, 

 inconveniences, as in the whole animal kingdom, but it cannot 

 be denied that all other organs taken as exclusive characters 

 offer still greater inconveniences. Thus the shell may be wanting 

 in very similar animals (for example, Notarchus, Aplysia ; 

 Pterotrachea, Cardiopoda ; Limax, Tebennophorus . The oper- 

 culum is often wanting in the adult, although the young may 

 have it. There are even operculated and inoperculated species 

 in the same genus, as understood by many modern authors (for 

 example, Pleurotoma and Bela, Oliva and Olivella, Yetus, 

 Voluta and L3a'ia, Spirialis and Limacina, Proserpina and 

 Helicina). The organs of respiration and locomotion may be 

 entirely wanting in closely related species (Firoloidea and 

 Phyllirhoe). 



Loven has characterized the families according to the teeth, 

 and has given Latin diagnoses. In 1848,Troschel {Handbook of 

 Zoology) mentions the teeth as characters of all his suborders, 

 and introduces into the nomenclature, for the first time, several 

 new names taken from the form of the teeth. Thus the section 

 H. of Loven is called Rhipidogiossa, including the Scutibranchs, 

 that is to say, Neritidse, Trochidse, Haliotidge and Pissurellidse. 

 For the section L. of Loven he proposed the term Toxogiossa. 

 Tseniogiossa corresponds to the Ctenobranchous Gastropods, 

 having seven rows of teeth (3. 1. 3.), excepting the operculate 

 pulmonates, although they may have the same form of teeth. 

 Thus Cyclostoma is placed in another suborder from Valvata 

 and Paludina. The Heteropods, which have the same general 

 disposition of the teeth as Tiienioglossa, are regarded as an order, 

 with the same value as the Gastropods — an opinion still main- 

 tained b}^ this author. 



In 1853, Dr. Gray (Proc. Zool. Soc, 32), in adopting the names 

 of Prof. Troschel, proposed several new groups, according to 

 the form of the teeth. 



1. Hamigiossa. Three ranges of teeth (1. 1. 1 ), the lateral 

 versatile. This last character appears to Prof. Morch to be 



