Report on the zoological collections made in the Indo-Pacific Ocean ...

120 COLLECTIONS FEOM MELANESIA.any one of the three collected by the officials of that great circumnavigatingexpedition.Though the term Plturechhins is due to L. Agassiz, and the specificname hothryoides to his incomplete comprehension of the Cidarishotlinjoides of Klein and Leske, I have confined my " synonymy "to Alexander Agassiz's <strong>Report</strong> on the ' Challenger ' specimens, asit is there only that any such definite information is given as wouldenable a zoologist to recognize examples of the species. The resultto which my own study of the specimens and of the definitions hasled me has, I think, been essentially confirmed by the investigationinto the structure of the test which, at my suggestion, Prof. MartinDuncan was allowed to make *.Looking, first of all, at the general form of the test, the observeris struck by its greater proportional height ; thus we find specimenswith an absolute diam(!ter of 20, 18, or 17 millim. respectivelyhaving a proportional height of 58-5, 66-6, and 60. Inno known examples of any other species of Temnopleurus is theproportional height more than 03-63 millim. f, and this is a rarecase, which obtains with a specimen only 11 millim. wide. Theexamination of the dental apparatus did not shov/ any real point ofdifference between this species and T. hardwicl-ii. As in otherspecies of this genus, the abactinal area is much more prominentin younger than in older specimens, while the characters of thefurrows between the plates is only intermediate between the extremecondition presented by T. toreumaticus and that which isBeen in the species just mentioned.As to the minute construction of the test. Dr. Duncan finds that" there is a generic relation between Temnopleurus and Pleurechmns,and the only important distinction is the absence of crenulation inthe last-named type." To this crenulation or its absence Dr. Duncanattaches more importance than do many naturalists who have devotedthemselves to this group, and he finds in consequence that " theclassificatory position assigned by A. Agassiz to Plmrechinus in the' Eevision ' must be conceded, and it is a subgenus or section ofTemnopleurusr Notwithstanding the weight of the authority ofAgassiz and Dimcan, I am bound to say that I feel still the importanceof the objections long ago urged by D'Archiac and HaimeJ," Quant aux crenelures des tubcrcules, on sait que cette particulariten'a cgalement qu'une valeur tres-secondaire, puisqu'on la voit dejadisparaitre dans une certaine portion du genre Cidaris, sans qu'onpuisse decouvrir chez les especes a tubercules lisses aucune autredifference concomitante; " and that being so, I can find no reasonwhich will justify the retention of a genus never very accuratelydefined.The largest specimen in the Alert ' ' collection has a diameter* Journ. Linn. Soc. (Zool.) xvi. p. 447.t P. Z. S. 1880, p. 424.X Anim. fo^s. de I'lnde, p. 202 (ISr^S). The student should be remindedthat Prof. Martin (Notes Leyd. Mus. ii. p. 75) accepts the genus Plcurcchinus.