704 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxn. 



largest, the others being graduated toward proximal edge of crown. 

 Theel's figure" shows a contracted imperfect specimen. 



Polian vesicle single, about 15 to 25 mm. long in medium sized 

 specimens, slender. Madreporic canal rather conspicuous, lodged in 

 dorsal mesentery, and running forward to enter body wall imme- 

 diately between the two anteriormost, long dorsal papillifi. There 

 appears to be no enlarged madreporic body such as Theel describes 

 for asper. Ring canal and proximal portions of radial canals promi- 

 nent. Calcareous ring rudimentary, consisting of slight deposits of 

 lime in the tissue. Gonad composed of two small tufts on either side 

 of dorsal mesentery immediately behind ring canal. Tubules short, 

 simple, clavate. Genital duct runs forward just above madreporic 

 canal, opening to the exterior b}^ either one or two small papillae 

 usually situated just posterior to the two large dorsal tentacles. 

 Longitudinal nmscle bands douhle, rather slender. Ampulla of 

 pedicels and papillae have the csecal appendage in body cavity short, 

 usuall}^ unbranched, except in largest individuals. 



One of the conmionest forms of spicules of dorsal perisome is that 

 shown by fig. 1, Plate LXXVII, which ranges from 0.55 to 0.8 mm. in 

 length. The number of branches varies, some having fewer, others 

 more than shown in figure. Size of perforations also is variable. 

 Rods of other shapes («, 7>, c) are essentially like the first, only slen- 

 derer. Average lengths for a, />, and <? are 0.6, 0.5, and 0.4 mili., respec- 

 tively. They vary considerably in length. The four-armed rods, 

 recalling those of Scotodeima setigerum-i are numerous, and range from 

 0.35 to 0.5 mm, in length. More or less perfect triradiate fojms with 

 equal arms are common, as well as forms intermediate with straight 

 rods {e) about 0.6 mm. long. In the region of the lateral tentacles 

 forms intermediate between figs. 1 and 2, la and 2rt, Ic and 2^, c^, 6, 

 may be found, or either the one or the other, this being the region 

 of transition between the dorsal and ventral surfaces. The ventral 

 perisome is characterized hy much heavier and more crowded depos- 

 its, especially toward the posterior end, where the relatively very 

 large ellipsoids and dumb-bell rods are massed together as thick as 

 possible, forming sometimes more than a single layer. Characteristic 

 forms of rods are shown by figs. 2 to 2e', these gradually passing into 

 such predominating forms as 3, 3ci, 3(', in posterior third of ventral 

 surface. Sometimes the latter forms predominate over the whole 

 ventral surface, the slenderer rods taking second place. These ellip- 

 soids are highly characteristic of this species, and conmionly attain a 

 size of 0.9 by 0.6 mm., varying down to 0.3 mm. in length. The 

 largest are irregularly spiny along one side and the surface is irregular. 

 The proportion of ellipsoids varies in different individuals; usually 

 various sizes of 3a, 2J, and 2(/ and intermediate forms predominate, 



"Challenger Holothurioidea, Pt. 1, pi. xliv, fig. 3. 



