OCR Text |
Show 412 ON THE ECHINODERMS OF MACCLESFIELD BANK. [May 1, than half an inch in diameter, shows that the form of the test is at first circular rather than decagonal. So far it bears out the remark of Prof. Alex. Agassiz, who, speaking of Peronella orbicularis, says (Eev. Ech. p. 521), " I have but little doubt that this species will prove to be the young of Peronella decagonalis "; at any rate, the series shows that when sufficiently small specimens are obtained they differ in form from the adult. Whether the type of Leske's species corresponds with any one of these I a m unable to say. I sent the drawing here reproduced to Prof. Selenka at Erlangen, as I imagined that Leske's type was in the University Museum therel. Dr. Pleischmann, who was kind enough to attend to m y letter in Prof. Selenka's absence, says :-" Das Originalexemplar zu Echinodiscus orbicularis war, wie ich den alten Catalogen entnehme, niemals in Erlangen. Wie besetzen nur Originalexemplare der Kleins'chen Sammlung." Leske compares his specimen with a Zeeschelhng, and M r . Grueber, of the Department of Coins, who has been kind enough to measure a Zeeschilling for me, tells m e it is '65 inch in diameter. The specimen here drawn has about that diameter, but has already ceased to be truly orbicular. It is impossible, therefore, to speak certainly, but I think we may safely take it that L. orbiculare is the young of L. decagonale; this at any rate is certain-a set of specimens collected on Macclesfield Bank form a continuous series, of which the smaller are circular and the larger decagonal in form. ARACHNOIDES PLACENTA. Echinus placenta, Linn. Syst. Nat. x. (1758) p. 666. Though commonly taken in distinctly southern waters as those of N e w Zealand and Australia, this species has already been recorded from Luzon, and is known as far west as Burmah and Mergui. Not only therefore has it a wide intertropical range, but it is found south of the tropics ; it is to be regretted that on p. 171 of the ' Alert' Eeport I put a sign against the name of this species which indicated that it was not known south of the tropics. EXPLANATION OF THE PLATES. PLATE XXIII. Fig. 1. Eudiocrinus granidatus, to show the habit of the species, X 2. 2. A portion of an arm from above (joints 14-20), X 6. 3. The most proximal joints of the arm, with their pinnules, X 4. 4. The seventh pinnule, to show the form and ornamentation of the joints, X 12. 5. One of the most distal pinnules, X 12. 6. A cirrus, X 4. 7. The distal joints of a cirrus, X 12. P L A T E XXIV. Fig. 1. Antedon bassett-smithi X 2, showing the disc and the bases of the arms with Sz, the first brachial syzygy, varying in position. 2. Side view of arm of do., X 2. 3. A cirrus, X 2. 4. 1st pinnule, to show the form of the joints, X 4. 5 & 6. 2nd and 3rd pinnules, to show the form of the basal joints, x 8. 1 See Agassiz, Rev. Ech. p. ix. |