APPENDIX. 349 



from the second) Prof. Gill uses the name Rhipidoglossa,. char- 

 acterized by the development of numerous hooklets or uncini 

 upon either side of the central and few lateral teeth of the lingual 

 ribbon (vol. i. PI. xii, f. 43-50). But this character is not coex- 

 tensive with the order Scutibranchiata, although nearly so, and 

 is besides of doubtful importance. Rather than use it in combi- 

 nation with a modification of the extent and characters of the 

 Scutibranchiata, I prefer to suppress that order entirely, as 

 Fischer has done, and as I originally intended to do (vol. i, 

 p. 82). 



In the case of Helicina, which possesses the dentition and 

 form of shell of the scutibranchs, there is an external sexual oro-an 

 in the male, thus alljang it with typical pectinibranchs. This 

 and the other land mollusks provided with opercula, and in 

 which the branchiae are represented by a network spread upon 

 the walls of a pulmonary chamber, are by some systematists 

 made a separate order, Pneumonopoma, connecting the pectini- 

 branchs with the Pulmonata ; they are closely connected through 

 Ampullaria, etc., as well as by their opercula and bisexualitj'^, 

 with the former. 



The second suborder of scutibranchs, the Bdriopthalmse, are 

 distinguished from ordinar}^ pectinibranchs by their conical 

 shell, but vary greatly among themselves in dentition (the 

 Patellidse, etc., being docoglossate (vol. i, PI. xii, f. 51), and 

 in the form and position of the branchiae (vol. ii, 326, 329, 330, 

 331, 332). 



The limits of the order Pectinibranchiata should be enlarged 

 to include the non-spiral shells and variously situated gills of the 

 limpets, and the aberrant, pneumonopomous, operculated terres- 

 trial mollusks, 



I annex Fischer's classification : 



Class Gastropoda. 



Subclass UnivalvJa. 



Androgyna. 



Order 1. Pulmonata. 



Order 2. Opisthobranchiata. 



Dioica. 



Order 3. Nucleobranchiata (Heteropoda). 



Order 4. Prosobranchiata (Platypoda). 



Subclass Multivalvia. 



Order 5. Polyplacophora. 



CoLUMBELLA, Lam. fp. 178]. 

 MiTROLUMNA, Bucq., Dautz. et DoUf., 1883. Proposed for a 

 group of shells uniting the characters of Mitra and Columbella : 

 no operculum. Type, Columbella Greci, Phil. Mediterranean. 



