109 



or in Waldheimia, be cut off and transferred to a glass plate, it may 

 readily be examined microscopically with high powers, and it is then 

 easily observable that its fibrous investment is a completely shut 

 sac. In Rhynchonella the enlarged caecum is often full of diatoma- 

 ceous shells, but it is impossible to force them out at its end, while 

 if any aperture existed they would of course be readily so extruded. 

 However anomalous, physiologically, then, this caecal termination 

 of the intestine in a molluscous genus may be, I see no way of 

 escaping from the conclusion that in the Terebratulida (at any rate 

 in these two species) it really obtains. There are other peculiarities 



Fig. 2. 



about the arrangement of the alimentary canal, however, of which I 

 can find either no account at all or a very imperfect notice. 



The intestinal canal (figs. 1 and 2 b, d, e) has an inner, epithelial, 

 and an outer fibrous coat ; the latter expands in the middle line into 

 a sort of mesentery, which extends from the anterior face of the 

 intestine between the adductors, to the anterior wall of the visceral 



