38 LITERATURE OF THE MOLLUSCA 
only in the Devonian, and the Dibranchs (Belemnites) at the 
beginning of the Secondary. But at the present day all the species 
of Tetrabranchs, some 7500 in number, are only represented by 
a few species of the single genus Nautilus; and as for the group of 
Belemnites, it has entirely disappeared since the end of the 
Cretaceous, its sole surviving and more or less distant represent- 
ative at the present day being the genus Spirula. 
Among the Gastropods the Aspidobranchs (Rhipidoglossa) are 
the first to appear; several families, such as the Capulidae and 
Pyramidellidae, date back to the Upper Silurian. On the other 
hand, there are but few Ctenobranchs in the Palaeozoic ; most of 
the families of this order make their appearance in the Secondary, 
and the same may be said of the Opisthobranchs, with the 
exception of the Actaeonidae, which are found, as also are the 
Pulmonata, in the Carboniferous. Of Lamellibranchs various 
Protobranchs and Filibranchs are found in the Silurian, but the 
other groups, as a rule, do not appear till the Secondary. The 
Palaeoconcha of the Primary, and the Rudistae, Diceratidae, Mono- 
pleuridae, and Caprinidae of the Secondary, have died out without 
leaving descendants. 
LITERATURE OF THE MOLLUSCA GENERALLY. 
I. Conchological. 
. Cooke. Molluses. The Cambridge Natural History, vol. ii. 1895. 
. Fischer. Manuel de Conchyliologie, 1887. 
Jeffreys. British Conchology, 1862-1869. 
. Simroth. Mollusca. Bronn’s Klassen und Ordnungen des Thierreichs, 
Bd. ii. 1895 till now. 
5. Taylor. Monograph of the Land and Freshwater Mollusca of the British 
Isles, 1900 till now. 
6. Tryon. Manual of Conchology, 1878 till now. 
7. Woodward. A Manual of the Mollusca, 1880. 
oo Nh 
Il. Morphological. 
bis. Cuénot. L’excrétion chez les Mollusques. Arch. d. Biol. t. xvi. 1899. 
7 
8. Geddes. On the Mechanism of the Odontophore in certain Mollusca. Trans. 
Zool. Soe. London, vol. x. 1879. 
9. Huxley. On the Morphology of the Cephaious Mollusca. Phil. Trans. 1853. 
10. von Jhering. Vergleichende Anatomie des Nervensystemes und Phylogenie 
der Mollusken, Leipzig, 1877. 
Die Gehorwerkzeuge der Mollusken, Erlangen, 1876. 
12; Zur Morphologie der Niere der sog. ‘‘ Mollusken.”’ Zeitschr. f. wiss. 
Zool. Bd. xxix. 1877. 
13. Lankester. Mollusca. Encyclopaedia Britannica, 9th edit. vol. xvi. 1883. 
Contributions to the Developmental History of the Mollusca. Phil. 
Trans. 1875. 
15. —— Note on the Coelom and Vascular System of Mollusca and Arthropoda. 
Quart. Journ. Micr. Sci. vol. xxxiv. 1893. 
