. Echinoidea. Sea urchins. ECHINOIDEA. II. 47 (Panamic Deep-Sea Ech. p. 163) to tlie genus PilniiaticJiiims established tliere for Cystech. Rathbuni. â A few remarks 011 the forms mentioned above maj- be given liere. Cystcchiuiis cLypeatiis. In the description of this species ( Cliall. -Ech. p. 149) Professor Agassiz remarks that in the specimens from the greater depths |ca. igoo fathoms) the test is niucli thinner than in the fragments which are found near the 1000 fathom Hue . This mav perliajss be true for other species (Agassiz refers to Pourtalrsia. Cystechiuiis and Urrchiiiiis), though I
. Echinoidea. Sea urchins. ECHINOIDEA. II. 47 (Panamic Deep-Sea Ech. p. 163) to tlie genus PilniiaticJiiims established tliere for Cystech. Rathbuni. â A few remarks 011 the forms mentioned above maj- be given liere. Cystcchiuiis cLypeatiis. In the description of this species ( Cliall. -Ech. p. 149) Professor Agassiz remarks that in the specimens from the greater depths |ca. igoo fathoms) the test is niucli thinner than in the fragments which are found near the 1000 fathom Hue . This mav perliajss be true for other species (Agassiz refers to Pourtalrsia. Cystechiuiis and Urrchiiiiis), though I do not see an\' such difference among the specimens of U. naresianns from the Ingolf-; but as for C. clypeatns the difference in the thickness of the test is in an\- case not alone due to the different depth at which the specimens lived, but also to their being different species, as I can state after having examined the fragments preserved in tlie British Museum; the pedicellariæ differ so considerabh- that it seems quite impossible that they can belong to the same species. Also the strncture of their apical sys- tems will probably be found to differ considerabh'. In the description it is said: The abactinal system closely resembles that of Cysfcchinus Wyvillii: the genital piates are, however, proportionalh- larger, the left anterior and the right posterior far exceeding the others in size, and extending entirely across the abactinal area, the whole central part of which is formed by the junction of the genital piates . But the figure, PL XXXV. b. 10, is, as will be seen, not in accordance with that description; the left anterior and right posterior genital piates do not exceed the others in size or extend entirely across the abactinal area, and the whole central part is not formed by the junction of the genital piates, the large ocular piates of the anterior paired ambulacra separating widely the anterior and posterior genital piates. â Among the fragments of Cystccltii
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Keywords: ., bookcentury1900, bookcollectionbiod, bookdecade1900, bookyear1903
