SPONGES. 231 



represents a small portion of the actual skeleton as it appears 

 at the surface of one of the specimens from the same locality. 



These figures, I believe, show in a reasonably clear manner 

 that we are dealing with a Lithistid sponge of the Tetracladina 

 type. The spicules are distinctly four-rayed, though the fourth 

 ray is much less developed than the others and rarely is more 

 than a mere stump. 



In the typical Tetracladina the rays of the spicules diverge 

 from a center at angles of about 120. In Hindiathe rays are 

 similarly disposed, but the regular arrangement of the spicules 

 into superimposed radial series so as to form tubes, appears 

 not yet to have been noticed in any other genus of the family. 

 It is a feature in which the genus may be said to simulate the 

 Anthaspidellidae. 



The individual spicules have, as has been stated, four rays or 

 arms extending from an inflated center. Three of the rays are 

 nearly straight, of nearly equal length, with their extremities 

 expanded mostly in a vertical direction. By their union a tripod- 

 shaped body is formed from the upper surface of which the short 

 fourth ray projects. 



The connected structure of the skeleton is easily understood 

 after we have once determined the true form of the individual 

 spicules. In the first place the spicules form rather regular con- 

 centric layers, in which the individuals are arranged alternately 

 so that any portion of each spicule is placed directly over or 

 beneath the corresponding portion of the spicules of the third, 

 fifth, seventh and ninth layers. The stumpy fourth ray is 

 always directed toward the exterior, while the three tripodal 

 rays extend toward the central nodes of three adjacent spicules 

 of the layer immediately beneath. The upper portions of the 

 expanded terminations in each case clasps about one-third of 

 the fourth ray of the latter, while the lower portion extends 

 downward in a recurving manner to the node or fourth ray of 

 the spicule directly beneath itf. This process is carried on inde- 

 finitely, so that while each spicule is connected by three rays 



+ According to Dr. Bauff, the terminations are toothed and the junction of the spicules 

 effected by the interlocking of the dentate portions. Although my material does not 

 permit me to corroborate his observations on this point, I am not by any means ready 

 to assert that he has misinterpreted the appearance of his specimens. 



