648 PROF. V. J. BELL ON THE GENUS PSOLUS. [NoV. 14, 



IIypopsolus, subgen. nov. 



It is necessary to institute a new subgeneric division for a remark- 

 able form, of which a complete account cannot be given, owing to 

 the fact that there is, unfortunately, only a single specimen. The 

 following, however, are important distinctive characters. 



The covering-plates are mostly of large size and of considerable 

 thickness, the whole covered by a rather thick integument, in which 

 there are some calcareous deposits ; the trivium is almost completely 

 occupied by suckers. Tentacles ? (retracted). 



PsoLus (Hypopsolus) ambulator, n. sp. (Plate XLVIII. 

 fig- 2.) 



There are six, not very regular, rows of large plates; at the edges 

 there are a number of small scales, imbricated in the manner so 

 common in the genus. The large plates extend round the base of 

 the oral covering-plates and behind the anus ; there are four or five 

 plates in most of the rows ; the large plates are of very various 

 shapes ; and though there are signs of a tendency to, there cannot 

 be said to be any imbrication. The mouth and the anus have the 

 positions ordinarily seen in other species of the genus ; the five 

 triangular oral plates are of very large size ; but the five found round 

 the anus are of a particularly small size. Many of the large plates, 

 and of the orals, have one, two, or, in rare cases, three small pores 

 on their integument ; when the plate is laid bare, the pore is found 

 to be the orifice of a small pit in the substance of the plate itself: 

 the function of these plates cannot be even guessed at, their small 

 size almost precluding us from the supposition that they are of a 

 marsupial nature ' — unless we suppose also that the present speci- 

 men is a male, or, in other words, a specimen in which the character 

 is only faintly indicated. 



On the trivial surface there are five or six rows of suckers in each 

 lateral ambulacrum, and as many as ten in the median one ; at 

 either end the mediau is continuous with the two lateral ambulacra, 

 and for the rest of the flat surface is separated from them by a 

 narrow, bare, corrugated band. 



Measurements. 



mm. 



Length of trivial surface 68 



Breadth of trivial surface 3.5 



Height of anterior end 31 "5 



Height of posterior end 16 



Size of some large plates = 12 X 10 mm. ; 11 x 8 ; 9 X 6. 



Hab. Australia. 



Limits of the Genus. — It will be seen that I have established a 

 subgeneric division for the reception of a form remarkable for the 

 thick covering of integument which is found over the large plates of 



^ Can they be compared with the perforations " for the passage of an ambu- 

 lacra! tube," found in a form allied to Fsolus. See Sir Wjv. Thomson, ' Nature,' 

 vii. p. 388. 



