OCR Text |
Show 1879.] MR. F. J. BELL ON THE ECHINOIDEA. 253 tubercles in different species, to be a character of value. Thus, in M. grandis there are large and distant tubercles, not only within the peripetalous fasciole and in the anterior ambulacra, but also over very nearly the whole of the actinal surface. In M. ven-tricosa the large tubercles on the abactinal surface are much rarer, and there are, especially along the ambitus, smaller and more closely packed tubercles; the larger and more distant tubercles are confined more to the anterior end of the actinal surface than they are in M. grandis. In Brissus the large and distant tubercles are completely absent from the posterior end of the abactinal surface, while on the same surface in Metalia the large tubercles are confined within the peripetalous fasciole ; and, further, in Metalia ster-nalis they only occupy the margins of the interambulacra. The example of M. ventricosa in the Museum collection is particularly fine. Though obtained in April 1847, it does not figure in Dr. Gray's Catalogue (1855). It was registered under the name of Amphidetes (sic) gigas, and is reported to have come from Brazil. I found some difficulty in determining it until I lit on the elegant diagnosis given by Prof. Grube of Brissus panis1. As to the identity of the British-Museum specimen with B. panis of Grube I have no doubt; the subjoined details will show some points of resemblance. I add some measurements of Meoma grandis :- Meoma ventricosa. Brissus panis. M. grandis. (B.M.) (Grube.) (Gray's type.) millim. millim. millim. Long axis 177*5 162 ( = 6 German 115 inches) Transverse axis 152 135 ( = 5 G. i.) 103 Height 82 81 ( = 3 G. i.) 51 Anterior pair ambulacra 80*80 .. .. 51*53 Posterior „ 91*88 .. .. 59*60 Length of anal system 21 .. .. 17'5 Breadth „ 17 .. .. 15 I am not inclined to dispute Liitken's view of the identity of Grube's species with Meoma ventricosa, Lamarck. The number of spines preserved on the specimen is fairly good; of those on the abactinal surface I found the greatest length to be about 8 millims.; but I measured one on the actinal surface which reached 12 millims. (Grube's longest spine measured 3 lines). The spines on the ambulacra are somewhat longer and thicker than those on the interambulacra, and are so set horizontally as to bridge over the ambulacral grooves ; they are in all cases of a whitish colour, and are not produced into sharp points. The madreporic plate is not less porous than in M. grandis. Grube had no information of the locality of his specimen; the most southern locality given by Agassiz is Honduras. 1 Grube: " Diagnosen einiger neuen Echinodermen," Arch. f. Nat. 1857, pp. 340-344; " Beschreibungen neuer oder weniger bekannten Seesterne und Seeigel," Nova Acta, torn, xxvii. (Jena, 1860). |