228 AMERICAN JOURNAL 



chiata, including two families ; (1.) Retifera for the Patellidoiy 

 and (2.), Branchifera for Fissurella, Parmaphorus and Emar- 

 ginula. He also unfortunately transferred the chitons to his 

 "Sub-type" Malentozociria, which last was composed of the 

 Cirriped crustaceans [Nematopoda] and the Chitons {Polyplaxi- 

 phora). 



Rang in 1829 considered the Patellidce and Chitonidce as form- 

 ing an order, for which he adopted Cuvier's name Cyclohranchi- 

 ata. 



Later, Gray (Guide to the MoUusca, 1857), placed the Lim- 

 pets in two sub-orders — Cervico- and CyclohrancJdata forming^ 

 part of his order, Scutihranchiata^ sub- division Heteroglossa. 

 The CervicobrancMata, however, contains two families, the 

 Gadiniidce and the Lepetidce, which cannot be affiliated with the 

 typical members of the group. 



The Messrs. Adams (Gen. Rec. Moll. 1858) however, must 

 receive the palm for combining under one sub-order [Edriopthal- 

 ma, but x\ol^=^Edriopthalma, Grray) of the ScutibrancJdata, a more 

 heterogeneous collection of families, including the Limpets, than 

 any other author (except their copyist, Chenu) hns dreamed of 

 doing. It cannot be said that any of these classifications were 

 an improvement upon that of Ferussac. 



In 1861 (Wieg. Arch. II) Dr. F. H. Troschel proposed for 

 the group of which the Limpets are the typical examples, the 

 term Pocoglossa, or plate-toothed. This was more fully defined 

 by him in 1866, in the first part of the second volume of the 

 " Gebiss der Schnecken," page 10. Though what would appear 

 to be a want of appreciation of other and equally important cha- 

 racters, however, the Chitons and l)entalia were included in the 

 same order, as by some previous authors. The same group was 

 adopted by Moerch under the name of Heteroglossata and di- 

 yided into the Cyclohr and data i. e. Patella, Chiton; and the 

 Cirrihranchiata viz., Dentaliwn. 



In the present state of our knowledge in regard to the embry- 

 ology and anatomy of Dentalium and Chiton, these views can 

 no longer be maintained, and the two groups indicated by these 

 names in their widest sense, will take rank henceforth as dis- 

 tinct orders. 



The order Pocoglossa, as here restricted, was first recognized 

 by me in a " Revision of the Classification of the Mollusca of 

 Massachusetts," (Proc. Bost. Soc. Nat. Hist, xiii, p. 245, March, 

 1870), at which time only the characters of the sub-order Abran- 

 chiata had been fully worked out. Since that time I have inves- 

 tigated the characters of the sub-order Proteobranchiata as here 

 restricted, and, in a paper read before the Am. Assoc. Adv. Sci., 



