426 Mr. G. C. Robson on the 



the lieail is usually not very much protruded beyond tlie shell, 

 though one can generally see the eyes. The buccal mass can 

 be seen working backwards and forwards if the animal is 

 biowsing. The coloration is variable. S{>ecimen3 have been 

 found almost colourless, with two narrow bands of black 

 pigment luiming backwards from the base of the tentacles. 

 More usually this pigment is very dense on the head, muzzle, 

 and upper and anterior parts of the foot, while on the sides 

 and back t>f the foot it is less well develoj)ed. The foot-sole 

 is ijivariably colourless except for the stripes referred to by 

 Smith, 



Contrary to Smith's statement, the animal is frequently 

 seen floating on the surtace-film (y. anon under "Pedal 

 Glands"), and ou one occasion it was observed to make use 

 of this facidty in a peculiar fashion. If it is turned over on 

 to the back of its shell it usually rights itself by rolling the 

 front of its foot backwards over its head, getting a foothold, 

 and pulling itself over by a leverage of the foot on the right- 

 hand side of the shell-aperture. One was being prevented 

 from doing this^ when it suddenly stretched its foot upwards 

 to the surface of the water and drew itself away from the 

 detaining needle by this method. 



Internal Anatomy. 

 The only substantial account of the anatomy of this genus 

 of which the author is aware is by Henking (5) upon Hydrobia 

 [=Paludestrina] ulvve, Pennant, llenking's paper and the 

 present account do not cover the same ground, but, where 

 possible, full comparison is made between the two forms. 



The Alimentary Canal. 



The mouth, when viewed transversely, ])resents the same 

 general features as li. ulvcc. The oral cuticle is not developed 

 10 the same thickness, however, while the vertical depth is 

 great(;r in F. jenlcinsi. The oral musculature docs not corre- 

 spond with that tigured by llenking, the small dilators ("'3) 

 shown by him being absent in P. jtnkinsi. Separate elements 

 corresponding with llenking's lip-protractors are found. 



The ;cnt'5 are sitiuited much as in P. idvd'. llenking does 

 not describe them in detail. In P. Jenkinsi they consist 

 of about ten to twelve rather irregular columnar pieces of 

 specialized cuticle, ol which the median are the largest 

 (PI. XV. lig. 1). 



Behind these the mouth expands laterally and is flattened 

 dorso-ventrally over the Unyiutl cart'iUiyes. C)wing to the 

 thick investment of muscle and the consequent ditiiculty in 



♦ In a watch-glass full of water. 



