423 Ml-. <1. < '. Robson ou the 



Tor Cydosloma (4). These ridges are sometimes of consider- 

 al>l»^ length. 



The crystalline style (PI. XV". fio-. \\) Hts closely into its 

 Siic and is a relatively large cylindrical body of hyaline 

 appearance, usually with rounded end-!. No attachment to 

 the cuticulcir lining of the sac could be found. After ex- 

 traction it invariably disperses in the fluid into which it is 

 jj laced. 



The hepatopancreas, which extends from the apex down 

 to the penultimate whorl, opens into the posterior chamber of 

 the stomach by a single broad and short duet near to and 

 on the same side as the opening of the oesophagus. 



The mtesdne leaves the pylorus and curls round the entl 

 of the style-sac to its anterior face, runs backwards along- 

 side the sac till it reaches the face of the posterior chamber 

 of the stomach, when it turns vertically and then runs 

 forwards to the anus. The intestinal wall is folded into a 

 well-defined typhlosole, which extends almost up to the pylorus. 



Pedal Gland. 



A well-developed pedal gland is present. It is possible 



that it is by the aid of the secretion from this gland that tiie 



animal adheres to surface-films. Among other freshwater 



Ttenioglossa such a gland has been described for Valvata (12). 



The Respiratori/ and Circnfatory St/stetn. 



There is a single monopectinate gill (Pi. XV. fig. 5) lying- 

 somewhat diagonally in the mantle-cavity, with its anterior 

 extremity between the tentacles and its posterior extremity 

 rather to the left ; it therefore lies roughly parallel to the 

 rectum. Its filaments* diminish gradually in size anteriorly 

 and posteriorly, those of about the median thiid being much 

 larger than the rest. 



It is almcst impossible in sections of a whole animal 

 to make certain that the gill-filaments are cut exactly 

 transversely; but from examinalion of a large number of 

 preparations it would seem that in F . jenkum they are more 

 lanceolate in section than in P. idvo'. The suppoiting 

 nu'Mibranes of the filaments are very long and thin. 



'J'hero is evident no modification of the gill or mantle- 

 cavity, although the animal is able to live out of water for at 

 least several hours. No positive trace of a hypobranchial 

 gland could be found. 



The heart lies in a capacious pericardium, which is situated 

 in the usual ])Osition. The auricle lies in front of the 

 ventricle and is smaller than the latter; its walls, as usual, 



* Twentv-sereu to thirty in number. 



