114 



proportionally, than in Waldheimia. They exhibit only a few longi- 

 tudinal folds, and not only present the same deficiency of muscular 

 fibres as those of Waldheimia, but are so tied by the bands which 

 support them that it is difficult to conceive how muscular fibres, even 

 if they existed, could act. The 'ventricles' in like manner lie ob- 

 liquely in the parietes of the body, and simply present villous emi- 

 nences on their inner surface, which has a yellowish colour. 



All these ' hearts' exhibit the same curious relation with the geni- 

 talia in Rhynchonella as in Waldheimia ; that is to say, a ' genital 

 band' (I) proceeds from the base of the ' ventricle' and becomes the 

 axis of the curiously reticulated genital organ. But in Rhynchonella 

 the genital bands of the upper genitalia come from their own 

 ' hearts.' 



The arrangement of the genitalia in Rhynchonella is very remark- 

 able. The sinuses have the same arrangement in each lobe of the 

 mantle. The single trunk formed by the union of the principal 

 branches in each lobe opens into the inner and anterior angle of a 

 large semilunar sinus which surrounds the bases of the adductors, 

 and opens into the visceral cavity. The floor of this great sinus is 

 marked out into meshes by the reticulated genital band, and from 

 the centre of each mesh a flat partition passes, uniting the two walls 

 of the sinus, and breaking it up into irregular partial channels. 



There are the same anastomosing bands uniting the gastro-pa- 

 rietal and ilio-parietal bands on the stomach in Rhynchonella as in 

 Waldheimia, and a pyriform vesicle of the same nature, but I did not 

 observe in Rhynchonella those accessory vesicles upon the origins of 

 genital bands, which I observed once or twice in Waldheimia. 



I could find no trace of arteries terminating the elongated, ovoid 

 and nearly straight ' ventricles' of Rhynchonella ; their ends appeared 

 truncated, and as I have already said, repeatedly presented a distinct 

 external aperture. 



Such appear to me to be the facts respecting the structure of the 

 so-called hearts in the Terebrat ulidee ; what I believe to be an import- 

 ant part of their peripheral circulatory system, has not hitherto, so 

 far as I am aware, received any notice. 



In Waldheimia the membranous walls of the body, the parieto-in- 

 testinal bands and the mantle, present a very peculiar structure ; 

 they consist of an outer and an inner epithelial layer, of two corre- 



