CLASSIFICATION. 255 



consequent upon the rapture of the tissues ; it is observed above 

 all when there is abundance of water under the compressor. 



2. Odontogiossa. Including only Fasciolaria, Mitra and 

 Turbinella, which have the same form of teeth, but of which the 

 laterals are not versatile. 



3. Rachiglossa. A single row of teeth (0. 1. 0.) ; the laterals 

 having disappeared. 



4. Dactyloglossa. Only differing from Tc«nioglossa by their 

 lateral teeth, which are wider, with very profound comb-like 

 incisions. 



5. Ptenoglossa. Teeth nearly subulate, in numerous longitu- 

 dinal rows ; Scalaria, Acteon. 



6. Gymnogiossa. No teeth : Architectonidae, Acusidse, Cancel- 

 lariadte, Pyramidellidse. But teeth have been since discovered 

 in the three first families. There are, doubtless, many genera 

 indubitably- deprived of teeth, without, for that reason, forming 

 separate groups. 



Gra}^ has regarded these different groups as having a systematic 

 value inferior to that of the form of the proboscis. Thus he 

 divides the Ctenobranchiates into two suborders : the Probos- 

 cidifera, which he believes zoophagous, furnished with an entirely 

 retractile trunk, and the Rostrifera, having a contractile, but 

 not retractile, trunk, and sometimes very long, as in Struthiolaria, 

 W'hich he supposes phytophagous. 



The author has thus placed the sections of Toxoglossa, G^^m- 

 noglossa, Ptenoglossa and Taenioglossa in these two suborders. 

 The small value of the retractile trunk as an ordinal character 

 is proved for example in the Bullidge {Bulla vexillum possessing 

 a very long retractile trunk). Odostomia has also a veiy long- 

 retractile trunk ; and the rather short trunk of Janthina is vei'v 

 often retracted into the head. 



In his Guide to the British Museum, 185*7, Dr. Gray has 

 reunited all the Toxoglossse in a single division Toxifera, still 

 retaining for the other divisions the separation into two widel}' 

 removed sections. The name of Cteuogiossa is changed to 

 Ptenoglossa ; the name Trapezodonta is proposed for the Corio- 

 cellae, the teeth of which do not appear to Prof. Morch to differ 

 from the Tseniogiossge except in the want of the two internal 

 teeth on each side (1. 0. 0. 1. 0. 0. 1.). Heteroglossa is proposed 

 for the Cyclobranchiates. 



In 1854, Morch divided the cephalophora into five great groups, 

 namel}' : I. Rhipidoglossata (including the Cyclobranchs) ; II. 

 Ptenoglossata (Pulmonata, Tectibranchiata, Janthinidse) ; III. 

 Tsenioglossata (including Pneumonopoma and Heteropoda) ; 

 IV. Hamigiossata (P^oboscidea of Troschel, Odontogiossa and 

 Rachiglossa of Gray) ; Y. Toxoglossata (including Pleurotoma 



