DESCRIPTION OF GENERA AND SPECIES. 
PiEROPODA, Cuvier. 
THECOSOMATA, cle Blainville. 
Pterocephala, Wagner, 1885. 1 
Eupteropoda, Boas, 1886. 2 
THE GENERA AND FAMILIES OF THECOSOMATA. 
In the Systematic Report on the Gymnosomatous Pteropods, I have noted a number 
of genera formerly included in the group Pteropoda, but which ought long ago to have 
been relegated elsewhere. 
Among the Thecosomata too, a number of forms have been rather recently included 
which do not belong to the group of Pteropods. Such are, for instance, Cheletropis and 
Sinusigerci, which are really larvae of Streptoneural Gastropods, whose velum has been 
mistaken for a fin ; 3 and as to Hcdopsyche ( Euribia and Psyche ), it is one of the 
Gymnosomata, as I have noted in my previous Report. 
But even after abstracting the names of genera which ought without hesitation to be 
removed from the systematic nomenclature of Thecosomata, there remains a long list of 
titles, which have been invented for living forms realty belonging to the Thecosomata, 
but of which the majority cannot be retained. Such titles are proportionately more 
numerous than the generic names established for the Gymnosomata, and this because the 
generic diagnoses of the Thecosomata have been almost always based upon the shell. 
To this, which is nothing more than a simple ectodermic secretion, conchologists have 
attached too much systematic importance. There are indeed certain subgroups of 
Thecosomata, including a number of generic titles, greater than that of the genuine 
species. 
1 Die Wirbellosen des weissen Meeres, Bd. i. p. 119. 
2 Spolia atlantica, p. 179. 
3 Gastropods of the family of Csecidae also have long been considered as Thecosomatous Pteropods, under the title 
Odontidium. 
