1869.] On tlie genus OncMdium. 109 



The internal organisation does not essentially differ from the type. 

 The oesophagus is comparatively small, the alimentary canal rather 

 long and thick ; the liver extensive and deep greenish ; stomach 

 very muscular and large. The internal vas deferens is very thin, 

 yellow, ahout three inches long, and twisted round the penis which 

 is about T 8 oth of an inch long, very thick, but otherwise not offering 

 any distinctions. Its supplementary albuminous string is thick, 

 white, and at least 12 inches long, it almost occupies one-third of the 

 body cavity just behind the head. The hermaphrodite organ is not very 

 extensive, the large albuminous gland of a purplish colour ; ovarium 

 deep, yellow ; testis white, small albuminous gland yellowish white ; 

 the vas deferens, issuing from the testis, is very thin, accompaning 

 the strong and thick oviduct ; the receptaculum seminis is represented 

 by a small, oval, dark coloured gland, closely attached to the oviduct. 



The nervous ganglion behind the oesophagus is particularly large, 

 sending numerous branches in all directions. The dentition is also 

 similar to the other species, the centrals have a very small point, and 

 the laterals form distinct hooks with an upright point at the end. 



The softness of the body, its great height, the peculiarly formed 

 tubercles of the mantle, and the situation of the pulmonary, herma- 

 phrodite and male genital openings, are the characteristic distinctions 

 of this species. 



It has been found, at the end of the rainy season, — in September 

 and October, — on the banks of the Mutlah river at Port Canning, 

 but appears to be rare. Its habits are peculiar ; it burrows in 

 mud, sometimes several inches deep, and appears on the surface 

 merely after, or during, the rain of a warm day. This evidently 

 accounts for the softness of the body. A few specimens which I kept 

 in a glass instantly burrowed in the soft earth, lying in holes in an 

 oblicpie or perpendicular position with the posterior tip of the mantle, 

 where the pulmonary orifice is situated, exposed so as to permit free 

 access of air. They sometimes did not appear on the surface for many 

 days, except when covered up and then placed in the sun. 



