REMARKS, ix 
ASPIDOBRANCHIA, CTENOBRANCHTA, and NevroBraANcuHtA (‘ Pulmonifera operculata,’ 
H. and A.Adams). It is not our object here to enter upon any discussion of the value 
of these various divisions ; but looking first at the PRosopocEPHALA, or SCAPHOPODA, 
it is evident from Bronn’s treatise (loc. cit. pp. 528-564), that many of the 
characters of the Dryrarrmx, as the presence of tentacles ( though numerous) 
on the head, the close connection of the foot with at least a portion of the digestive 
organs, the unilateral opening of the genital organs, the teeth on the radula and 
others, are in many respects the same as those in the largest number of other 
GastropopA. It is true that, according to the latest researches of Lacaze- 
Duthiers and Sars, the Dewrazipz appear to be in many respects of a much lower 
organization than had been previously believed. It is said that they have no heart, 
nor any special respiratory organ, and that the entire surface of the body, not 
attached to the shell, acts as the latter, although this last statement does not appear 
to be satisfactorily proved as yet. We have among other Gasrropopa also many 
instances of a very low organization, for we meet with species, which have no 
heart, and consequently no regular circulation (in Rhodope of the OpIstHoBRANCHIA) ; 
others which have no mouth or special organs of respiration (many GymMNosomATA 
of the HereropopA), and still, looking to the totality of the organization, we cannot 
but retain these and other forms in the respective orders, or families, to the species 
of which they are in other respects closely related. 
_ Comparing, on the other hand, the five sub-orders of the Prosoprancuta, the 
assemblage appears to us rather heterogeneous; and we would suggest to exclude 
from them the first and the last, namely, the POLYPLACOPHORA, (( CuironrpD#), 
and the NrvROoBRANCHIA, classing these as separate orders, equivalent to the 
Prosoprancnia. Both are entitled to this rank; the former by the want of 
tentacles and the articulated shell, and the latter by the respiratory organ, and con- 
sequently different mode of life. We would then have, as formerly acknowledged, 
only two divisions inthe CEPHALOMALACTIA, namely, CEPHALOPODA and Gas- 
tropopA. The latter could then be further divided into eight orders: 1, Pumo- 
NATA; 2, NEUROBRANCHIA; 3, PROSOBRANCHIA; 4, HeErTeropopa ; 5, PoryeLaco- 
PHORA; 6, OPISTHOBRANCHIA; 7, PrmERoPpoDA; 8, PROoSOPOCEPHALA. 
In the course of our descriptions, we shall retain this classification, although 
only four of the orders, the PutmMonatTa, PRosoBRANCHIA, OPISTHOBRANCHIA and 
PROSOPOCEPHALA, (or ScaPHoropa), will occupy our special attention, because of the 
other orders no representatives have as yet been discovered in the South-Indian 
eretaceous rocks. 
