OCR Text |
Show 648 PROF. F. J. BELL ON THE GENUS PSOLUS. [NOV. 14, HYPOPSOLUS, subgen. nov. It is necessary to institute a new subgeneric division for a remarkable 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 specimen 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 median 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 35 Height of anterior end 31*5 Height of posterior end 16 Size of some large plates = 12 x 10 m m . ; 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 1 Can they be compared with the perforations " for the passage of an ambulacral tube," found in a form allied to Psolus. See Sir W y v. Thomson ' Nature ' vii. p. 388. |