LYTECHINUS DYSCRITUS. 249 



triphyllous are very small and are common. The valves measure about .15 mm. 

 in length and are two thirds as broad. The sphceridia are spheroidal or less 

 commonly ellipsoidal ; they occur only on the actinal part of the ambulacra and 

 five or six may be grouped at the peristome. They seem to be perfectly smooth. 



The coloration of this species is variable only in the amount of green. The 

 general appearance of both test and spines is creamy white, while the plated 

 buccal membrane is clear white. Abactinally, particularly along the sides of 

 the interambulacra, there is a more or less marked shading of light green; in 

 some specimens this is very marked, while in others it is almost wanting. Above 

 the ambitus, the primary spines are as a rule, light green at base fading out into 

 white at the tip. In some specimens, the spines are mostly green, but usually 

 the white greatly predominates. 



This interesting species was collected by the "Blake" in the West Indian 

 region, but the specimens were identified either as Trigonocidaris albida or as 

 Toxopneustes variegatus, although in most cases the doubtfulness of the identifica- 

 tion was indicated on the label by one or more question marks. The resemblance 

 of small specimens to Trigonocidaris albida is very marked, the absence of the 

 sculpturing of the test being the only important difference, although the differ- 

 ence in color is more or less evident. From Lytechinus variegatus, this species 

 is easily distinguished by the exsert oculars and the very short primary spines, 

 as well as by the coloration. The geographical range of euerces as indicated by 

 the "Blake" collection is from the Gulf of Mexico, northwest of the Tortugas, 

 to Barbados, but three fourths of the thirty-nine specimens are from the vicinity 

 of St. Lucia and Barbados. The bathymetrical range is from 84 to 300 fathoms. 



Lytechinus dyscritus, 1 sp. nov. 

 Plates 93, fig. 10; 96, figs. 1-3. 



The larger of the two available specimens, which are nearly of a size, is 7 mm. 

 in diameter and only 3 mm. high. There are 8 interambulacral plates in each 

 column and 9 ambulacral. The longest primary, from the ambitus, is about 

 5 mm. long. The abactinal system is 3 mm. in diameter and the actinostome is 

 3.5 mm. across. 



The periproct (PI. 96, fig. 3) is rather large, distinctly bigger than a genital 

 plate and is covered by 4 or 5 large plates, of which the one adjoining genital 3 



= hard to determine. 



