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Hawaiian and Other Pacific Echini

Hawaiian and Other Pacific Echini

139514064
1100 руб.
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Описание
Excerpt from Hawaiian and Other Pacific Echini: The Salenidae, Arbaciadae, Aspidodiadematidae, and Diadematidae

The guadrideniaz'e pedicellariae (pi. 45, fig. 1) are much less common than the tridentate, and are only known to occur in three species. They are usually found on the actinal part of the interambulacra. The head is shorter than the stalk, sometimes very much so, and there is practically no neck. The valves (pls. 45, fig. 2; 46, figs. 1, 2) range from about three fourths Of a millimeter up to two millimeters in length and are straight and commonly more or less ?at. They may afford useful specific characters. Doderlein found one of these pedicellariae with five valves, but we have never seen more than four.

The ovoid pedicellariae (pi. 45, fig. Are not very common, but are usually to be found on the interambulacra. The head (p1. 45, fig. 18) is about one fourth of a millimeter long, and is attached to the stalk by a neck Of about the same length. The stalk itself is three to six times as long as the head. The three valves (pls. 45, figs. 5, 12, 23; 46, figs. 5, 6) are all alike and are dis tinctly longer than broad. They commonly lack an articular loop on the base, but this is occasionally present. For this reason, they seem to us to be modified ophicephalous pedicellariae, while D'oderlein considers them to be small tridentate. They are undoubtedly comparable to the triphyllous pedicellariae of other Echini, but are hardly sufficiently modified to be called by that name.

The globose pedicellariae (pi. 45, fig. 6) are usually common and often abundant, and are to be found on all parts of the test, though they are most frequent on the ambulacra and about the abactinal system. There are Often five groups of them present on the buccal plates in large specimens. The head is about one-fourth of a millimeter in length, and the stalk is usually about the same, though it may be twice as much there is no neck. The valves (pls. 45, figs. '7, 13, 19, 22; 46, fig. Are provided with an articular loop on the base, but as this is never very large, those of the same head do not differ appreciably from each other. The valves are short and deep, rounded at the tip, and about as wide as long. While there are usually only three, pedicellariae with four such valves are occasionally to be found. In spite of the small size of the articular loop, there is no reason to doubt that these globose pedicellariae Of the Salenidae are Ophicephalous.

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