LYTECHINUS PICTUS. 259 



The series at hand ranges from 5 to 40 mm. in diameter. In the full-grown 

 specimens, the height is clearly more than half the diameter. The abactinal 

 system (PI. 99, fig. 7) is rather small, only about .25 h. d. The actinostome is 

 also small, about .35 h. d. Oculars I and V are well insert, but in most of the 

 small specimens, ocular V is more or less fully excluded. The adult character 

 in this respect seems to be acquired when the individuals are between 15 and 

 20 mm. in diameter. The buccal membrane (PI. 99, fig. 6) is heavily plated in 

 all the specimens, except the largest, where more or less resorption has occurred 

 and the membrane is visible between the plates. Coronal plates are numerous; 

 in a specimen 20 mm. h. d., there are 14 interambulacral and 17 ambulacral 

 plates in each column, and in the specimen, 40 mm. h. d., there are 21 and 30 

 respectively. The gill-cuts, though well defined are not deep, even in the largest 

 specimens. The primary spines are short, the longest ones only about one 

 fifth the diameter of the test. Pedicellarise are only fairly common. The 

 globiferous were found in both young and old ; the valves range from .50 to .60 mm. 

 in length and have the usual tubular blade and long end tooth; the blade may 

 be constricted, just above the broadly expanded base. The ophicephalous are 

 fairly common; the valves of those found in the large specimens, are about 

 .60 mm. long, nearly triangular, and not at all constricted, while in the young 

 specimens, the valves are only about .35 long, they are distinctly constricted 

 and the lime of which they are composed is strongly tinged with brown. The 

 tridentate were found only in the large specimens. They closely resemble those 

 of Toxopneustes (Plate 93, fig. 7); the valves measure .30-1.00 mm. in length. 

 The triphyllous are fairly common, but very small; the valves measure about 

 .15 mm. in length by .13 mm. across the blade. The sphceridia are very numer- 

 ous, for although they do not extend far up the ambulacra from the peristome, 

 as many as twenty may be found at the base of a single ambulacrum; of course, 

 in the young they are far less abundant. They are not peculiar in either size 

 or shape. The spicules in the tube-feet are arcuate but not bihamate, the ends 

 being blunt or almost knobbed. 



This species has hitherto been regarded as the young of some larger species. 

 The specimens received at the Museum of Comparative Zoology have usually 

 been labelled Toxopneustes pileolus or Tripneustes depressa. The structure of 

 the ambulacra shows conclusively that these identifications are wrong. Although 

 nearly related to L. semituberculatus, there is not the least superficial resemblance 

 to that species. On the other hand, except for differences in color, the resem- 

 blance to L. verruculatus is noteworthy. 



