286 Mr. W. H. Dall on a Natural Arrangement 



female, and tliey were soon connected, and the claspers were 

 inserted to the base. 



The claspers of the snakes are covered with a number of 

 slender spines on all sides, and they may often be seen pro- 

 truding at the sides of the vents in specimens in spirits ; and 

 specimens with them so protruding are figured by Seba and 

 other iconographers. Mr. Ford informed me that in the puif- 

 adder the claspers are dark brilliant reddish purple, covered 

 with abundant white recurved spines. 



XXXVII. — Sketch of a Natural Arrangement of the Order 

 Docoglossa. By W. H. Dall*. 



The following is a preliminary sketch of a more natural 

 arrangement of the Mollusca contained in the orders Cervico- 

 BRANCHIATA and Cyclobranchiata of Gray, taken from the 

 results of investigations now in preparation for publication in 

 a more extended form. These investigations having shown 

 that no line can be drawn between the two orders of Gray 

 above mentioned, it follows that they must be consolidated ; 

 and for the group in question the order Docoglossa, Troschel 

 (minus the Pohjplacojyhora and Solenoconchoi) ^ has been re- 

 stricted and adopted. As the denominations previously ap- 

 plied all imply an erroneous idea of the structure of the ani- 

 mals, this course has been determined upon in preference to 

 using prior, but incorrect, ordinal names. 



The order, as here restricted, was first recognized by me in 

 ^' A Revision of the Mollusca of Massachusetts " (Proc. Boston 

 Soc. Nat. Hist, xiii, p. 245, March 1870), at which time only 

 the characters of the suborder AhrancJiiata had been fully 

 worked out. Since that time I have investigated the charac- 

 ters of the suborder Broteohranchiata^ as here restricted ; and 

 in a paper read before the American Association for the Ad- 

 vancement of Science, at Troy, September 1870, of which a 

 synopsis was published in the 'American Naturalist ' (Novem- 

 ber 1870, p. 561), I restricted the order Docoglossa within its 

 present limits, from the researches above mentioned. Among 

 the fruits of these investigations was the definite exclusion of 

 the Gadiniidoi from the order (see Am. Journ. Conch. 1870, 

 vi. p. 8). It is proper to state that Prof. Theodore Gill had, 

 upon general considerations, adopted the same limits for the 

 order in his unpublished manuscript, although the conclusions 

 to which I have been led were the result of independent ana- 



* From the 'Proceedings of the Boston Society of Natural History,' 

 Feb. 7, 1871. Commuuicated in advance by the Author. 



