ANIMALS. 79 



at, when comparing the former with the vascular impressions of Leptana and OrtJds, 

 there seems httle remaining to prove that the paUial 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 psittacea, 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, Biscina, Criopus, and Terebratula (e. g. caput-serpentis), in 

 which there is no appropriate apophysary system,^ warrant us, however, in cautiously 

 weighmg 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 PI. XIX, fig. 2 e). In their 

 position and form, these impressions forcibly remind one of the horizontal, spirally- 

 folded, labial processes of Biscina and Criopus. It may be noticed, in passing, that 

 if the reniform lobes on the flat valve q{ Productus had sustained the labial appendages, 



' Monographic du genre Productus, 1847. 



* The loop in Terebratula caput-serpentis is naainly a visceral support. 



