46 
THE VOYAGE OF H.M.S. CHALLENGER. 
This classification has been adopted in Fischer’s 1 Manual of Conchology, and in 
part also in that of Try on. 2 
It is however necessary to remark that Fol distributes these four genera in a manner 
altogether peculiar, separating most of the species from the group at present under 
discussion. Thus in our family of Cavoliniidse (his Orthoconques) he distinguishes, ab- 
stracting the genus Cuvierina, three subgroups, — Hyaleacees, Styliolacees, and Creseidees. 
Hyalocylix is referred to the first, along with the Cavolinia forms. Styliola and 
Cleodora are included in the Styliolacees. Creseis is placed among the Creseidees. 
I cannot admit that these different forms are separated in this way, or in any way 
equally deep and trenchant. 
Fol’s distinctions, which are based exclusively on embryonic characters, form an 
insufficient foundation for the classification of the adults. For it must be noted that the 
forms in question are pelagic larvae in which, as Fritz Muller long ago remarked, 3 true 
genetic characters are mingled with those which are merely adaptive, and provisionally 
acquired for the free, independent, pelagic larval life. 
On the other hand, the different forms of Clio exhibit a type of structure which 
unites them in one and distinguishes them from the other Thecosomata, and especially 
from the “Hyaleacees” of Fol (among which the “ Cleodora ” forms are certainly more 
nearly allied than the Hyalocylix). 
Nevertheless, it cannot be denied that among the species which I have united within 
the genus Clio there are several distinct types, separated not only by the embryonic 
differences on which Fobs classification is based, but also by certain structural features, 
which will be discussed in the anatomical portion of this Report. Yet, at the same time, 
I maintain that these distinctions are not of sufficient import to justify the establishment 
of separate genera. 
I therefore propose to consider the different types above referred to as subgenera 
of Clio, and since these subgeneric divisions correspond approximately to the genera 
recognised by Fol, I shall preserve as designations of these subgeneric sections the four 
titles which Fol has used, viz., Creseis, Hyalocylix, Styliola, Clio ( = Cleodora). As to 
Balantium, I do not find that it exhibits any characters which would warrant its being- 
separated from the subgenus Clio ( = Cleodora), s. str. 
Within these four sections, the species known to be genuine are distributed in the 
following fashion : — 
1. Subgenus Creseis. 
Creseis virgula, Rang. Creseis acicula, Rang. 
Creseis conica, Eschscholtz. Cleodora chierchise, Boas. 
1 Manuel de Conchyliologie, pp. 435-437. 2 Structural and Systematic Concliology, vol. ii. pp. 90, 91. 
3 Facts and Arguments for Darwin, p. 114. 
