23 181 



tioned they container] a more yellowish lens and a colourless vitreous corpus. The oto- 

 cysts had also a diameter of 0'l6 mm , the globular light yellowish otolith a diameter 

 of 0l0 mm . 



The buccal tube whose fore end was surrounded by a strong glandular layer, 

 had a length of (>75 mm . The small, scarcely l mm long, bulbus pharyngeus which was 

 enclosed by thick glandular masses, was of the common form, with the common transverse 

 half-rings on the dorsal side; posteriorly it was provided with the common, semilunar, 

 solid, somewhat flattened, crop-like process; below the globular radula bag was found. The 

 bulbus pharyngeus as usual chiefly formed by the large muscular mass of the tongue. 

 The upper series of tooth plates contained 7 developed plates and one undeveloped one ; 

 in the lower series 7 plates were found in a row, and the radula bag (the diameter of 

 which was 0.26 mm ) contained a very large number. The slight yellowish tooth plates were 

 of the common form, the hooks on each side mostly provided with 11 — 12 short, blunt 

 denticles (fig. 13). 



The globular follicles of the hermaphrodite gland contained ripe sexual elements. 

 The penis bag had a length of l - 2 mm ; the glans was provided with an almost cylindric, 

 slightly curved prickle, which only at the base was yellowish; it had an oval opening at 

 the end which, as it were, was obliquely cut off (fig. 14). 



Since the figure made by von Hasselt of his Plakobranchus ocellatus, has been 

 published ') (the original specimen is wanting in the museum of Leyden) , there can scar- 

 cely be any doubt that the PL argus, more exactly examined by me, is specifically iden- 

 tical with his species. The colour of this form appears to be varying to a high degree, 

 and several forms (PL ianthobaptus , Godld; PL gracilis, Pease; PL variegatus, Pease; 

 PL camiguinus, Bgh. , and perhaps still more) that have been established as species, are 

 likely to be only varieties of locality and colour. 



The form examined here, corresponds, with regard to the prickle of the penis, 

 perfectly with the PL argus. 



') R. Bergh, die van Hasselt'schen Nudilnanchicn. Notes from the Leyden Museum. IX. Note XLIII. 

 1887. p. 311. Taf. 6, Fig. 5. 



