ANIMALS. 17 
in Camerophoria. 1am only acquainted with the internal structure of Magas pumilus 
through the beautiful figures given of it by Mr. Davidson;! I can therefore only 
throw out the suggestion that the anterior part of the apophysis of this shell may also 
be a muscular fulcrum. 
One of the features which distinguish the Palliobranchs as a class from all other 
molluscs, is their branchial system. Instead of possessing a respiratory apparatus, in 
the shape of laminated gills, as in ordinary bivalves, both lobes of the mantle are 
rendered subservient to respiration, by means of numerous veins and arteries variously 
and minutely ramifying towards the pallial margin.” All the recent forms hitherto 
examined, have the mantle closely and strongly adhering to the inner surface of the 
valves; and, it is im consequence of this adhesion, that we occasionally meet with 
palliobranchiate fossils displaymg, in the most beautiful and imstructive manner, 
impressions of the vessels that conveyed the blood which circulated in the long-since 
extinct molluscs that inhabited them. 
Having succeeded in obtaining several specimens exhibiting impressions of nearly 
their entire vascular system, it has been deemed necessary to give some figures to 
illustrate a character of the greatest importance in the class under consideration. 
The figures representing casts of both valves of Camerophoria multiplicata (Pl. VIII, 
figs. 6, 7) instructively display the large veins (2) or returning vessels inclosing the 
arteries (j), described by Professor Owen as prevailing in the recent forms.* 
The specimens of Leptena analoga represented under figures 6 and 7 in Plate XX, 
show the impressions of the vascular system in a beautiful state of preservation ; but 
owing to the veins being obscured and confused near the anterior angles of the valves, 
it is impossible to say whether the main trunks passing along their medio-longitudinal 
region curve continuously round towards the centre of the hinge, or become confluent, 
where the obscurity prevails, with those which pass along, and forward from, the 
hinge-lie, supposing the latter to originate in the medio-cardinal region. From what 
is displayed on the figures of Camerophoria multiplicata, the former view seems to be 
the correct one. The cast of Zrzgonotreta undulata, under figure 6 of Plate IX (c), is 
the only specimen of the genus I have seen exhibiting the vascular system. 
Besides the vascular and muscular impressions, there are others, in certain genera, 
to which it is necessary in the next place to direct attention. The flat valve of 
Productus often exhibits two reniform impressions or lobes, each one striking off from 
between the pair of muscular scars situated on each side of the median plate (PI. XT, 
fig. 107; Pl. XIX, fig. 3 /),—an origin, which, to a certain extent, identifies them with 
the primary vascular trunks, issuing in a similar way (and occasionally subdividing into 
I Note sur le Magas pumilus; Bull. de la Soc. Geol. de France, 2™° série t. v, pl. ii. 
2 In Lingula the branchial system is somewhat modified. 
’ Transactions of the Zoological Society, vol. i, part ii. 
