new aiid Uttle-knoion Trematode.t. 52o 



encysted cercavia dosciibed by Professor M'liitosh * from 

 Carcinus nKenas n.nt\ Cancer fxifjurus. lie bases his assump- 

 tion on the close losembhxnce between the cerciiria and the 

 adult, and endeavours to correlate the various structures \n 

 them. He is possibly correct, but there is just as much 

 ground for assumiiiu" that Levinsenia from Lams is the adult 

 of the cercaria from Curcinus. The shape and the structure 

 show just as much resemblance. The occurrence of the 

 adult in such pjreat numbers corresponds, too, with the 

 exceptional frequence and abundance of the cysts in the crab. 

 Until proper feeding experiments have been conducted or 

 more accurate information is forthcoming the point must 

 remain in abeyance, though it is known that gulls and other 

 birds readily devour Carcinus and Cancer, e. g. after storms 

 on the West Sands at St. An hxws. 



Psilostohium redactum, sp. n. (PI. XIII. fig. 9.) 



From the intestine of the 3-spined stickleback {Gasterosteas 

 aciileatus) . 



The stickleback has been examined by several observers, 

 yet, although quite a number of parasites are described from 

 it, only two Distomidie, viz. JDistomum ventricosum and 

 D. appendicu/atum, have so far been recorded. 



Psilostomum redtictum is a small species of length 1 -lO mm. 

 The breadth is variable. Both anterior and posterior ends 

 are somewhat bluntly pointed. The widest parts of the body 

 occur at distances of about ^ of the whole length from each 

 end. The body narrows again in the middle. At the 

 broadest parts the bieadth is "45 mm. ; in the middle it is 

 •31 mm.; towards the end of the tail -18 mm. The surface 

 of the body is not armed witli spines, but the cuticle has 

 distinct loii;^Mtudinal and transverse striations. 



The oral sucker is suljterminal and circular, with a diameter 

 of '16 mm. The ventral sucker is elliptical, with the long 

 axis transverse; it measures "38 x "23 mm. The cuticle of 

 the ventral sucker presents a beautifully distinct reticular 

 striation. 



The mouth opens in the oral sucker and is continuous 

 with a large muscular jjharynx, '09 mm. broad. The gut 

 brandies into two diverticula immediately behind the pharynx. 

 The diverticula widen as they pass down, so tliat they assume 

 an almost sac-like shape, but towards the end they become 



* Q. Juur. xMicr. Sc, July \8()~), p. L'OO, pi. viii. 



