REPORT ON THE PTEROPODA. 
93 
a 
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Fio. 5. — Longitudinal section of 
the apex, a, of Tenlaculites, 
b, of Clio. 
2. Tentciculites. — These are the only Primary “ Pteropods ” on which one might found 
arguments in favour of an apparent resemblance to the subgenus Hyalocylix of Clio. 
Their external surface, indeed, presents grooves or rather trans- 
verse rings. Nevertheless, the comparison of median longitudinal 
sections of a Tentaculites and a Clio shows at once that the 
resemblance is only superficial, and that in reality the two 
organisms are quite dissimilar in structure. 
The Thecosomatous Pteropods such as Clio have a shell of 
almost constant thickness, and distended at the extremity (embry- 
onic shell of Fol). Tentaculites , on the other hand, ends in a 
sharply pointed extremity, and the thickness of the shell gradually 
increases from the aperture towards the apex. 1 
Jn the same way the supposed Devonian Cleodora (= Clio), described by Ludwig, 2 
has the apex like that of Tentaculites, and not at all like that of Clio. 
Among the other Primary “ Pteropods ” three principal groups may be distinguished — 
(1) Conulavia, (2) Hyolithes, (3) the Cymbuliidse described by Ehrenberg, Ecculi- 
omphalus, Portlock ( = Phanerotinus , Sowerby ; this was ranged by Bronn 3 among the 
Pteropods, but is really a Gastropod allied to the Solariidae). 
T. Conulavia. — These differ from all the Thecosomatous Pteropoda hitherto known 
in their quadrangular shell and contracted aperture ; even the structure of their shell 
separates them entirely from the Thecosomata. They have been placed along with these 
by d’Archiac and Verneuil, who, not being zoologists, were unacquainted with the 
organisation of the Pteropoda ; and in consequence merely of this allocation all paleon- 
tologists have continued to class Conulavia among the Pteropods. 4 
2. Hyolithes. — These are distinguished from all the Pteropoda by their triangular 
form, their partitions, and their operculum, which in no respect resembles that of any 
operculate Mollusc. I must also here allude to the case of Calceola sandalina, which 
was so long referred to the Brachiopoda, and which is only an operculate Polyp. 
Without committing myself to any opinion regarding Hyolithes, which I have not had 
the opportunity of studying personally, I may ask whether it may not be possible that 
this also is a species of operculate Polyp. 
1 Ludwig, Pteropoden aus dem Devon und Oligocan in Hessen und Nassau, Palseontographicn, Bd. xi. 
pi. 1 . 3b. 
2 Ibid. I must mention that the elongated Primary fossils with an initial dilatation resemble Dental iidse as much 
as if not more than Thecosomatous Pteropoda (compare M. Sara, Malakologiske Jagtlagelser, Forhandl. Vid. SelsJc., 1864, 
pi. viii. figs. 49-51, and G. 0. Sars, On some Remarkable Forms of Animal Life, &c., i. 1872, pi. iii. figs. 14, 15). Some 
similar Dentaliidae have been found in the Challenger soundings. This would furnish an argument in favour of the 
views of Grobben, who regards the Scaphopoda as very primitive forms (Morphologische Studien, &c., loc. cit.). 
3 Die Klassen und Ordnungen des Thierreichs, Bd. iii. p. 646. 
4 Lindstrom (On the Silurian Gastropoda and Pteropoda of Gotland, K. Svenslc. Vetensk. Akad. HandL, Bd. xix. No. 6, 
p. 40) insists that the septa of Conularia furnish a proof of its Pteropod nature, whereas not one of the living Thecoso- 
mata has septa of this character. 
