Mi croscopic al Essays. 



557 



140. Cercaria Tripos. Fig. 38, Plate XXV. 



Cercaria Tub triangularis, brachiis deflexis, cauda redla. Cerca- 

 ria fomewhat of a triangular form, two bent arms, and a ftrait 

 tail. 



The body flat, pellucid, triangular, each angle of the bale of 

 the triangle, or fore-part thereof, being bent down into two 

 linear ears, or arms ; the apex of the triangle is prolonged into a 

 tail. It was found in fait water; b the tail, a the bent arms. 



141. Cercaria Cyclidium. 



Cercaria ovalis, poftice fubemarginata, Cauda exterfili. This is 

 oval, the hind-part fomewhat notched, with a tail, that it thrufts 

 out at pleafure. 



It's body is oval, fmooth, membranaceous, pellucid, with a 

 black margin. ' The tail is not fixed to the edge, but concealed 

 under it, and coming out from it at every motion, and yet fo as 

 to project but little from the edge. There is a kind of border to 

 the hinder-part. It's inteftines are very pellucid veficles. Is fre- 

 quently found in pure water. 



142. Cercaria Tenax. 



Cercaria membranacea, antice craffiufcuia, truncata, cauda 

 triplo breviore. Membranaceous, the fore-part rather thick, 

 truncated, the tail three times fhorter. 



4 



It 



