280 Mr. W. Clark on Ancylus oblongus and A. fluviatilis. 



and divided by a depressed line which gives a bilobed aspect ; it 

 is ridged externally at the cardia, and within is furnished with 

 muscular fillets ; the intestine is simple throughout, and on 

 leaving the pylorus winds to the dexter side, terminating just 

 within the respiratory cavity. The liver is a large pale greenish- 

 yellow granular mass, deposited below the muscle around the 

 upper part of the cone. 



The sac of viscosity is in close union with the pericardium, 

 inclining to the left of the dorsal region, the canal of which 

 from its minuteness escaped our research, but it doubtless is 

 concurrent with the intestine and rectum. The heart and 

 auricle, of pale yellow, are at the bottom of the left side of the 

 respiratory vault. The ovary at the apex of the spire, of a 

 yellowish-white colour, is attached to the hindermost lobe of 

 the liver, and presents the figure of a subrotund granular mass 

 or minute bunch of grapes, having a slender twisted or sinuated 

 white oviduct that enters the matrix at its lowest point. The 

 very small bladder is white, sometimes pale blue, elongated or 

 flask-shaped ; it floats by its long canal between the testicle and 

 matrix, and probably pours its contents into the latter, but the 

 extreme minuteness of the parts did not permit us to verify that 

 point. The testicle is a large granular mass, and can be seen 

 through the mantle, lying on the dorsal region posterior to the 

 heart and auricle, partially united to the lower portion of the 

 matrix, which is of very irregular diameter ; the vas deferens is 

 easily traced to the termination of the verge. 



The verge is under the right tentaculum and is retractile : we 

 have seen it in every phase : in the genial season it is large, 

 fleshy and subcylindrical. The orifice of the matrix is veiy con- 

 siderably below it, close to the valve of respiration. It is difiicult 

 to conceive how such a constituted animal should be mistaken 

 for a Pectin ibranchiate, unless, as is mentioned below, the 

 packet of parasites has passed for branchial filaments. The 

 mantellar collar, which is more or less an attribute of all the 

 Pulmonifera, is in the Ancyli a slender cord, plain on the left 

 side, but forms at the respiratory cavity a rather elongated nar- 

 row expansion or fillet, which we have often seen the animal 

 elevate for respiration, or to eject the fjccal rouleaus : when the 

 organ of respiration is opened, the network does not appear 

 greatly developed : the artery, vein, and the descending aorta 

 could not be verified. The heart and auricle are with difficulty 

 observed in the pericardium. 



The above observations show that this animal is a true Lini- 

 neadan : we do not pretend that they are without error, for it is 

 extremely difficult to separate and define the exact position and 

 precise form of the organs of so minute a creature. 



