APPENDIX. 



301 



Malacobdella grossa (page 35). 



Body 1^^ in. long, about Y%ths of an inch in breadth where 

 broadest ; oblong, flat, soft, exannulose, roughish, with little granu- 

 lations, and of a uniform flesh- 



No. L. — Malacobdella grossa. 



^^ 



a. Upper side. b. Under side. 



colour. On the upper side a 

 small vessel is seen distinctly run- 

 ning down the middle of the body, 

 having a tortuous course, and ter- 

 minating near the sucker ; and it 

 lies over a much larger intestine, 

 following the same direction, and 

 alone visible on the ventral aspect. 

 The anterior extremity is rounded, 

 somewhat raised above the mouth, 

 which is placed in a sinus here, 

 and opens chiefly on the under 

 side ; it is wide, edentulous ; but, 

 when opened, the inner surface 

 appears flocculent, being clothed 

 with longish papillae, which are arranged in close longitudinal series, 

 and cover the whole intestinal canal. This organ is nearly of uni- 

 form width and structure throughout ; but the papillae appear to be 

 longer towards its termination, which is by a small aperture on the 

 back, just above the sucker. The dorsal vessel begins in a sort of 

 swelling above the mouth ; and, after it has passed beyond the 

 middle of the body, it becomes sensibly attenuated. It is not 

 fibrous, and, indeed, exhibits no marked structure beyond a very 

 fine and faint reticulation of the surface when exposed under a high 

 magnifier. The space between the intestine and margins of the 

 body is compactly filled with myriads of oviform bodies, which seem 

 to lie, without any particular order, in a gelatinovis fluid : they are 

 roundish, opake, and encircled with a rim or pellicle of transparent 



I have twice found this leech in specimens of Cyprina islandica 

 dredged up in Berwick Bay. They were lurking between the cloak 

 and branchiae, and doubtless had sought out the site for a less harm- 

 less purpose than shelter from foes ; but, so far as I could judge 

 from external appearances, the oyster had not suftered any material 

 injury. 



On the suggestion of Lamarck, it has been here considered a species 

 of PlujUine ; but it will not correspond with the character of the 

 genus, for tlie large terminal disk or sucker is not armed with hooks, 

 as Lamarck's definition expresses, but is quite smooth. Nor has 

 the skin the slightest appearance of circular rings, or rugae, even 

 when contracted and hardened by spirits ; and its whole anatomy is 

 so unlike that of Annelides, and more especially of the true leeches, 

 that it strengthens an opinion of Lamarck's, of there being a class 

 of animals, yet unestablished, between the Annelides and the worms. 



