112 
THE GEOLOGIST. 
this interpretation of the origin of the reniform impressions, as he 
does not see liow they can have anything to do witli the vascular 
system, properly so called, and to which they have been attributed by 
various authors. They could uot possibly have been ^jroduced by 
pallial or ovarian sinuses ; for, if so, we should have expected to find 
them also in the ventral valves.* 
We will now add a few words relative to the probable mode of 
existence assumed by the Productidoe, and which does not appear to 
have been the same for all the species of which the family is com- 
posed. The opinion entertained by some palteontologists that the 
shell was suspended by muscular fibres issuing from tnbular cardinal 
spines, or from between the margins of the shell, are highly im- 
probable, and unsupported by any acceptable evidence. It is, however, 
probable that some of the species were free and unattached, while 
others show clear evidence as to their having adhered to marine 
bodies by the beak of their ventral valve {e.g. Strophalosia and 
Aulosteyes). D'Orbigny supposes that the animal of Froduda lived 
on soft sea-bottoms, lying with the smaller or dorsal valve uppermost, 
• In a letter I have recently received from Mr. Hancock, there is the following- 
passage : — " The idea that the renifonn impressions gave su]>port to the arms does 
not appear inconsistent with the opinion expressed by you and others, namely, 
that a portion of each arm was airanged spiially, and occupied tlie hollows in the 
ventral valve. I am (luite inclined to believe tliat these reniform callosities gave 
snjjport to the first or basal portion of the arms. The arms may afterwards have 
become free, and have formed more or less incomplete spirals, and may have fitted 
into the snlispiral cavities of the ventral valve in Prodacta yir/anfea, &c. In some 
other species no .s])irals may have been developed, and the extremities of the arms 
may liave been disposed hi some other manner. In Thccidium the terminal por- 
tions are variously aiTanged ; and this may have been the case in the Productidoe. 
It is impossible not to be strack with the resemblance of the reniform impressions 
in fig. a of your PI. IV., to the ridges supporting the arms of Thecidium in PI. VI. 
fig. 42, of yoixr General Introduction." 
Professor King exi)lains his views regarding the origin of the reniform impres- 
sions in the following words, which I think it well to rejiroduce in this place, that 
the reader may have before him the reasons adduced by those who would connect 
tlie above-mentioned impressions with the vascular system, a.s well as of those who 
attribute them to the ridges supporting the anus : — 
" Taking Leptcena analoga and Productus horrklus, as examples illustrating the 
cliaracterism of the vascular system of their respective families, it may be predi- 
cated of Strophomenidce, tliat the primary ])allial vessels are more or less confined 
to the medio-longitudinal region of the valves ; and of Productidce, that they 
strike off at tlie moment they i.ssue from between the muscular scars, in a lateral 
direction, running for some distance nearly parallel to the cardinal line, then 
curving forward and round towards the centre, and finally returning to nearly their 
origin. Looking at the vein-like line bounding the reniform lobes of Productus 
horridus [see the woodcuts] and P. semircticidatus, I cannot but think that these 
stnictures are each due to a recurving vessel, rather than to an expanded and 
simply projecting vascular organ, as appears to be the case in Criopus (Crania).'" 
