ANIMALS. 79 
at, when comparing the former with the vascular impressions of Leptena and Orthis, 
there seems little remaining to prove that the pallial structures, to which the pro- 
duction of the reniform lobes of Productus have already been assigned, were the genito- 
vascular organs of the animal. 
Seldom have any other traces than the reniform lobes been discovered of the 
vascular system of Productus. Dr. de Koninck, in his ‘Animaux Fossiles,’ figured 
the large valve of a species exhibiting, as he thought, impressions of vessels ramifying 
over its surface; later observations, however, have convinced him that these im- 
pressions have been caused by an Annelid.! A considerable number of specimens have 
passed under my observation, with the view of ascertaining the existence of vascular 
impressions, but, with one exception, the only appearance of the kind I have seen is 
on the flat valve of a Productus setosus, kindly given me by Mr. G. Tate, who procured 
it from the Carboniferous shales in the neighbourhood of Alnwick. What are taken 
for vascular impressions are two main trunks, each one laterally situated, running near 
the sides of the valve, and giving off outwardly, and at regular distances, numerous 
simple branches, which loose themselves in the margin. The specimen of Productus 
giganteus under figure 2, Plate XIX, may also be noticed as showing very distinctly 
one or more vascular impressions (d) originating in the region of the medial dendritic 
scars; and in their course repeatedly subdividing, and finally passing into the large 
striated lateral impressions: the producing vessels of these impressions have un- 
doubtedly nourished the superior pedicle muscles. 
Reverting to the labial appendages, it would scarcely be concluded, considering the 
soft and extensile nature of these organs in Hypothyris psitiacea, that they had ever 
left any traces of their existence in shells which had neither spirals nor a loop to 
support them: the rigidness and immobility of the labial appendages in certain 
existing genera, for example, Discina, Criopus, and Terebratulu (e. g. caput-serpentis), in 
which there is no appropriate apophysary system,” warrant us, however, in cautiously 
weighing all observed facts before assenting to this conclusion. The facts in question are 
certain impressions occasionally met with in Productus, and which it is proposed 
to refer to the pressure of the labial appendages ; it is in this view we must regard the 
pair of somewhat concentrically-furrowed hollows occasionally to be seen on the inside 
of the large valve of these shells, or the correspondingly marked prominences often 
displayed on casts of the same. M. Von Buch, who first brought forward this view, 
has already figured a specimen in the latter state; and I have been fortunate in 
obtaining another one showing similar characters (vide Pl. XIX, fig. 2¢). In their 
position and form, these impressions forcibly remind one of the horizontal, spirally- 
folded, labial processes of Discina and Criopus. It may be noticed, in passing, that 
if the reniform lobes on the flat valve of Productus had sustained the labial appendages, 
' Monographie du genre Productus, 1847. 
* The loop in Terebratula caput-serpentis is mainly a visceral support. 
