20 SALEXIA VARISPINA. 



These delicate processes appear, however, to be soon either worn ofY or 

 broken, as in specimens measuring from 2 to 3 mm. in diameter we generally 

 find only an occasional primary spine still retaining the filiform processes, or 

 a trace of them. As the spines become older, these processes are little by 

 little changed to the sharp spiny processes figured as characteristic of S. 

 varismna. The primary spines of these young stages are also marked for the 

 single prominent vertieillation formed near the base of the shaft by the some- 

 what stouter filaments of that portion of the radiole. 



The young spines found on the small primary tubercles near the abacti- 

 nal system on the ambulacral and interambulacral areas have a striking 

 appearance. They recall somewhat the fan-shaped, short spiny radioles 

 found on the test of very young specimens of Strongylocentrotus ; they also 

 recall the peculiar umbrella-shaped spines of Aceste, and of some deep-sea 

 Ophiurans. The primary spines, when the shaft has as yet but a single pair 

 of filaments, could readily pass for modified pedicellariae ; they also resemble 

 the hook-like appendages of the Ophiurans. In the next stage the radioles 

 carry from four to five processes, when the central part of the shaft begins 

 to increase in length ; with this increase commences also the formation of 

 the filaments, so characteristic of the large primary interambulacral spines 

 of the young stages. The primary interambulacral spines are usually simi- 

 lar, but shorter, slender-pointed radioles, with from six to eight processes and 

 a ring of filaments near the base of the shaft. In the youngest stages there 

 are as yet no papillae; these appear only later, in larger specimens, and at 

 first show no trace, in the interambulacral areas, of their regular Cidaris- 

 like arrangement round the base of the primaries, as in the older stages. 

 The papilhv when they first appear are short slender-pointed spines, with 

 short, sharp processes, covered by lines of pigment-spots of dark violet. 

 With the growth of the test these papilla become club-shaped, curved, 

 and finally flattened and fan-shaped as they appear in the older Saleniae. 

 The papillae of the anal plates are articulated in the older specimens; at 

 first they are sessile, like the embryonic spines (club-shaped sessile papillae) 

 covering the plates of the genital ring; with the increasing size of the 

 young Salenia they resemble more the coronal papilla*. These abactmal 

 sessile papillae are interesting, as they develop exactly as do the embryonic 

 spines in young Echini, from the general granulation of the plates; but 

 they remain, as in the Arbaciada), always sessile. 



As 1 have stated, the genital openings are not yet formed in young speei- 



