414 ECHINOTHRIX CALAMARIS. 



less spreading at extremity, hollow for their whole length, and extremely 

 thin and delicate. The spines of older specimens frequently retain these 

 characteristics of the young until they attain quite a large size; generally, 

 however, with increasing age and size the spines become comparatively 

 more tapering and stouter. The test is intermediate between that of E. 

 turcarum and E. Desorii, having larger and more prominent tubercles than 

 the latter, but still with narrower coronal plates than the former. In the 

 interambulacral region the bare median space extends nearly to the ambitus. 

 There are but four primary tubercles to each coronal plate, few secondaries, 

 and the miliaries are more prominent and more numerous than in either 

 of the other two species. The scrobicular circle of the primaries is marked 

 and well defined, the primaries of the actinal surface gradually diminishing 

 towards the actinostome, which is proportionally larger than in the other 

 species of the genus. The actinal membrane is in the prolongation of the am- 

 bulacra, closely covered by large limestone plates. The ambulacra are broad, 

 the poriferous zone of median breadth, from three to four median rows of 

 secondary tubercles between the two outer ones. Ambulacra near the abacti- 

 nal system slightly raised, so that the test of both this species and E. Desorii 

 is slightly gibbous near ambitus, with flattened actinal surface and somewhat 

 conical outline towards the abaetinal pole, with depressed abactinal area. The 

 abactinal system is remarkable for the great size of the anal system, covered 

 by a thin membrane only strengthened by a lew limestone granules, a single 

 row of plates near the genital ring, and the small size of the cquilaterally 

 triangular genital plates separated by greatly elongated ocular plates. The 

 color of the spines varies from a uniform straw color to light violet-colored 

 spines, with four or five broad bands of a darker color; the test and am- 

 bulacra! spines being generally of darker tint. Crenulation of the tuber- 

 cles is quite indistinct, and in young specimens can scarcely be traced. The 

 actinal membrane of the young is thickly covered by plates, as well as the 

 anal membrane ; the outline of small specimens is also more globular. 



East India Islands ; Society Islands ; Philippine Islands. 



