'1870.] 49 [DaU. 



sented, imperfect as they must needs be, in the hope that they may 

 lead some of the members of this Society to give more attention to 

 this very interesting subject of study. 



Preliminary Sketch of a Natural Arrangement of the 

 Order Docoglossa. By W. H. Dall. 



The following is a preliminary sketch of a more natural arrange- 

 ment of the mollusca, contained in the Orders Cervicobrancliiata and 

 Cyclobranchiata of Gray, taken from the results of investigations now 

 in preparation for publication in a more extended form. These in- 

 vestigations having shown that no line can be drawn between the two 

 orders of Gray above mentioned, it follows that they must be consol- 

 idated; and for the group in question, the Order Docoglossa Troschel 

 (minus the Polyplacophora and Solenoconchce) , has been restricted 

 and adopted. As the denominations previously applied, ail imply an 

 erroneous idea of the structure of the animals, 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., xni, p. 245, March, 1870) at which time only the characters 

 of the suborder Abrancliiata had been fully worked out. Since that 

 time I have investigated the characters of the suborder Proieobranchi- 

 ata, as here restricted ; and in a paper read before the American 

 Association for the advancement of Science, at Troy, September, 

 1870, of which a synopsis was published in the American Naturalist, 

 (November, 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 Gadin- 

 iidce from the order. (See Am. Journ. Conch., vi, p. 8, 1870). It 

 is proper to state that Prof. Theodore Gill had, upon general con- 

 siderations, adopted the same limits for the order in his unpublished 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 anatomical investigations upon my part, 

 which, so far as I am aware, are the only ones, including the whole 

 order, which have been made. I am indebted to Prof. Gill for sug- 

 gesting the very appropriate names by which I have designated the 

 suborders as restricted. 



PROCEEDINGS B. S. N. H.— VOL. XIV. 4 JUNE, 1871. 



