ANIMALS. 115 
extremity; is concave on its upper surface; and has a ridge passing along its median 
line. The ridge forms the upper portion of a high vertical plate, which supports the 
spatula-shaped process, and extends from the under side of the crural base to within a 
short distance of the centre of the shell (Pl. VIII, figs. 3, 4, 57), and which is evidently 
the counterpart of the dorsal medio-longitudinal plate already noticed. (Vide 
ante, p. 70.) 
In order to ascertain the use of certain processes in Camarophoria, it will be 
necessary to turn our attention for a short while to some other shells of the same 
class. 
By examining casts of most species possessing dental plates separated from each 
other, it will be seen that the intervening space between these plates, from the scars 
thereon, has afforded attachment for certain muscles. Extending our researches to 
those shells in which the dental plates approximate more and more until they become 
united, as in certain Strophomenide,' it will be quite evident that the attachment of the 
muscles has been gradually removed from the surface intervening the dental plates, to 
that of the plates themselves when they became united. The scars visible on the 
saucer-shaped process of Leptena analago lead to the same conclusion. Now as there 
are no muscular impressions on the surface of the large valve of Camarophoria, and it 
being certain that its arch-shaped process has resulted from the union at their upper 
margin of the dental plates, it clearly follows that this arch shaped process has served 
as a muscular fulcrum. 
Turning our attention to casts of Hypothyris acuminata, or any of its immediate allies, 
there will be seen on the posterior half of the small valve, on each side of its median 
line, certain elongated impressions, which are obviously due to muscular attachment : 
this shell, it must be borne in mind, has no spatula-shaped process,—only the homologues 
of the two crura of the loop characteristic of Hypothyris (psittacea). Possessed of these 
facts, our attention is naturally drawn to the small valve of Camarophoria: but here 
we search in vain for any scars corresponding either in form or position with those of 
Hypothyris acuminata : they could not occur on the parts where they are situated on the 
_ Shell last noticed, in consequence of the spatula-shaped process overspreading them : this 
circumstance, and the fact that they are not visible on any part not overspread by the 
spatula-shaped process, or unoccupied by other structures, show that the muscles were 
nowhere attached to the surface of the small valve: hence it may be safely inferred 
that the spatula-shaped process of Camarophoria has been a muscular fulcrum—a 
conclusion powerfully supported by the elevated apophysis in the small valve of 
Leptena analago (vide Pl. XX, fig. 7 c,d) having been for a certainty a correspondingly 
subservient structure. 
The vascular system of Camarophoria appears to be nearly similar to that of 
1 Vide Geology of Russia, vol. ii, pl. xi, fig. 2a, and pl. xii, fig. 3 g. 
