1869.] On the genus Onchidium. 107 



yellowish white. The receptaculum seminis is a comparatively very 

 email globular capsule, the oviduct being, however, very strong, almost 

 horny ; the portion of the liver covering the end of the stomach is 

 cup-shaped and small ; the intestines and the rest of the liver normal ; 

 the penis above an inch long, with a setous flagellum ; the internal vas 

 deferens is about 5 inches, and its supplementary albuminous string 

 about 8 inches long, almost equally thin throughout. The pulmonary 

 cavity is large with numerous cross-folds, the lungs yellowish. The 

 heart is small, white, the aorta at the beginning not • much narrower, 

 the thicker branch going to the digestive organs. 



The radula is particularly narrow in this species, but the teeth are 

 very similar to those of Onch. typhca, the laterals being only a little 

 larger. 



This species is rather common along the banks of the Mutlah at Port 

 Canning, it is generally seen creeping about on old wood. It survives 

 a long immersion in brackish water, but shrinks and soon dies in sweet 

 water. I often found it in holes or at the roots of bushes on the bank 

 of the river during low water ; when the water rose the specimens must 

 have been fully for 8 hours submerged. The largest specimen, measured, 

 was two inches long, and about the middle 1 T 2 ^ of an inch broad. 



The broad, depressed form of the body, the narrow foot, thin eye- 

 pedicles and the solid coriaceous structure of the mantle, readily 

 distinguish this species from others. 



4.— Onchidium tenerum, Stol, Pi. xv, Fig. 3. 



The general form of the body is oval, more or less elongated, but 

 very high, it is remarkably soft, almost pulpy in fresh caught speci- 

 mens, always enveloped in a thin layer of secreted mucus. The 

 ground colour of the upper surface of the mantle is greenish grey, 

 irregularly mottled and spotted with dark. Two obtusely elevated, 

 somewhat undulating and pale coloured, ridges run from the edges 

 of the mantle above the eye-pedicles posteriorly near to the end, en- 

 closing a central area of the back, in which a number of very large 

 oval tubercles are situated. These are of a greenish colour, covered 

 with smaller warts, their tips being yellowish, and each of them provid- 

 ed with from 1 — 3 black dots. Pull grown specimens have besides a row 

 of similar large tubercles running externally and parallel to the ridges 



