OF SOUTHERN INDIA. 327 
provided with radiating ribs, like Patella; apex sub-central, obtusely pointed ; 
aperture more or less oval, or irregularly roundish, the margin generally being 
interrupted by the projecting ribbings ; the siphonal groove is usually placed in Front 
on the right side, and is on the external surface often marked by two closely placed 
ribs, which project beyond the margin more than the rest ; the muscular impression 
is interrupted on the siphonal groove. 
It is evident from these general characteristics, that the only shells related to 
Siphonaria are Gadinia and Deslongchampsia. The species are principally 
inhabitants of the tropical seas; they do not differ in their mode of living from 
Patelle, beng found between tide marks attached to rocks. They also often 
remain for some time above the low tide, and it is probable that on this account 
they develope a separate lobe with which to close the respiratory orifice, so as 
to prevent the drying of the gills. Such changes in the organization are by no 
means unusual, and they no doubt form the basis of all the distinctions which we 
have to trace out, and on which we base our classification of the orders, families and 
genera. It is not clear from the account given by Quoy and Gaimard (Voy. 
d’Astrolabe, Zool. Vol. II, p. 323, etc.) that the animals are really air-breathing, 
though they seem to be in some respect amphibious, like Ampullaria and others, as 
‘might evidently be expected from their mode of living. The lings or rather a 
portion of the respiratory sac is said to assume its functions when there is no 
sufficient moisture for the gills. In spite of these differences in the respiratory 
organs I do not think, that the family could be placed more naturally anywhere 
else than next to the Gupinizpm, Treoruripm and Leperipz. 
There are as yet only a few tertiary species of Siphonaria known, though 
some of them appear to have been described under the name of Patella. The 
first and only well known cretaceous species is the Siph. antiqua, Binkhorst (Gast. 
et Ceph., Limbg., 1861, p. 60, pl. 4, fig. 3; and pl. 5, fig. 5). We have not 
obtained any species from our cretaceous deposits in South India. 
IIIf. Sub-order,—Cyclobranchiata. 
PareLtin#, H.and A. Adams, Gen. I, p. 463; Gray, Guide, 1857, p. 173; Bronn, Klassen 
und Ord., Vol. III, p. 1034; Deshayes, An. s. vert. foss. de Paris, IT, p. 220. 
This small group of animals is characterized by the form and position of their 
gills, which are lamellar and placed on the inner surface of the mantle, between 
it and the foot. Gray’s remark that “the gills are only an elongated branchial 
plume springing from the neck”’, and that they “ ought not to be looked on as a pair 
of symmetrical, sub-semicircular lamin, as in the Cyclobranchiate Chitons,” 
is of great interest. It is true that the gills of the CycLoBraANcHIATA are not placed 
in a separate respiratory cavity, but there cannot be a question that they other- 
wise very much resemble those of some Yzcrvezpz; there are in fact instances 
where a distinct separation between the Cervicobranchiate—and the Cyclo- 
branchiate—form is almost impossible to accomplish; beyond certain limits 
