APPENDIX. 303 



not always present ; and the outer surface is either rugose or smooth. 

 Moquin-Tandon says that in P. verrucata the separating ring is 

 broader than those of the sets, and gives this as a part of the specific 

 character ; but this is not the case in my specimen. However, in P. 

 verrucata the division into sets is more obvious than in P. muricata. 

 The breadth of the rings varies according to the conditions under 

 which the leech has died, and affords no character. The form of the 

 papillae seems alone to distinguish the species. In P. muricata they 

 are prominent, rigid, and pointed, with the apex roughish with 

 spinules ; in P. verrucata they are much less elevated, with a broad 

 shield-like base, and a papilla in the centre ; and they are less 

 crowded than in P. muricata. The difference does not seem to be 

 specifical, and hence I include both species in these observations. 

 There is no very perceptible difference between the dorsal and ventral 

 surfaces. 



The observations of Dalyell are much in favour of the opinion 

 that there is only one species. It lays its ova within stalked cap- 

 sules which are attached to old shells, &c., and usually in groups. 

 "The capsule consists of a sole, a short stalk surmounted by a 

 spheroid, with a distinct umbo on the side. The capsule altogether 

 is about three lines, and the spheroid which contains the embryo, or 

 leech, about two in diameter. — Such capsules are firmly agglutinated 

 by the sole to the substance whereon they are deposited. They are 

 originally white, or of the faintest carnation, of a fine soft downy 

 aspect, with the neck orange or yellowish. They darken gradually 

 from the time of production, and in four or five days the original 

 white is converted to olive-green, or dull wax-yellow. They are pro- 

 duced singly, free of all gelatinous matter.*' — (p. 6.) 



"The capsule consists of a coriaceous, tough, thick integument 

 full of tenacious, albuminous, brownish matter. It contains only a 

 single embryo, which penetrates the lateral umbo in issuing forth to 

 the light. Then the young animal is about an inch in length.'' — 

 (p. 7.) 



It deposits the capsules chiefly during summer. 



PontobdeUa laevis (page 41). 



Hah. "Obtained alive in April 1838, either at Portpatrick or Do- 

 naghadee, by Capt. Fayrer, R.N., who commanded the mail steam- 

 packets between these ports." — W. Thompson. 



" Corps en longue massue, tres-attenue en avant, et ge renflant peu 

 ^ peu jusque tout apres de I'extremite posterieure, lisse, et meme 

 sans articulations distinctes ; ventouses terminales : la posterieure 

 fort petite ; Tanterieure assez peu considerable, sans traces de vermes 

 tentaculaires, ni de points pseudo-oculaires ; orifices des organes de 

 la generation tres-anterieurs, au premier sixieme environ ; anus fort 

 petit ; couleur d'un brun roussatre." — Blainville. To this descrip- 

 tion Blainville adds that his specimen was given to him by M. Paretto 

 of Genoa. It was, although preserved in spirits, upwards of half a 



