412 Mr. G. C. Eobson on tie 



Tlie upper part usually stains a li(>lit blue with liJBinatoxylin' 

 the lower part an intensely dark bluish purple. 



The author is inclined to regard the lower portion as a 

 uterus* or brood-pouch. Although it is tliick-walled and no 

 eggs have been found in it, its lower portion in its position 

 and relationship to the rest o£ the leproductive system 

 resembles organs adapted for tlie reception and nutrition of 

 the young, such as are found in neiglibouring groups. 



The spermalheca has a thick investment of circular muscle, 

 and is usually composed of elongate secretory cells with basal 

 nuclei. {Spermatozoa were found in numerous examples, 

 sometimes scattered throughout the cavity, sometimes clustered 

 round the sides with their heads towards the periphery. 



Affinities. 



Along with Ilypsohia Heude gave incomplete descriptions 

 of several new genera, such as l)elavaya, Ilemihia, and Fe- 

 nouilia, some of which show certain points of resemblance 

 to f/i/psobia. 



We have only a very slight knowledge of the structure of 

 the other Asiatic Paludestrina-Wke forms. The information 

 as to the European forms is a little more complete. It must, 

 tiierefore, be admitted that these resources are scarcely 

 adequate to enable us to form a clear concept either of the 

 natural groups into which the Paludestrinid?e (Hydrobiidge, 

 auct.) may be divided or of the limits of the family itself f. 

 Admitting, then, that the family may be rather indefinite in 

 its boundaries, it nevertheless cannot be doubted that the 

 characters of the alimentary canal (including mandibles, 

 cartilages, and ra^lula), nervous system, and genitalia at once 

 assign HypsoUa to the Paludestrinidse. In what subfamily 

 it should be placed is rather more uncertain. Some of its 

 characters suggest that it should take its place very near 

 Paludestrina itself, and at least in the same subfamily 

 (radula, mandibles, style-sac, nervous system, and male 

 genitalia). On the other hand, the specialized respiratory 

 system, the kidney, the female genitalia, and the character of 

 the spermatozoa do not seem to warrant its inclusion in the 

 PaludestriiiinaB. Yet among the adjacent subfamilies — Bythi- 

 niina?, Mysorellinas, &c. — there is none in which it might be 



* The upper portion may be an albumeu- or a shell-gland, but for the 

 time being the author prefers to call it the " accessory gland." 



t The writer has had uo opportunity of consulting Mr. B. AValker's 

 " Synoi)sis of the Classification of the Freshwater Mollusca of North 

 America," Mus. Zool. Michigan Uuiversit}', Misc. Publ. 6, 1918, p. 1. 



