E. MARSHALLI. — SPICULATION. 99 



thickness of 35 /i. The axial cross has been determined to be 

 (always ?) simple, that is to say, having a single cross-piece. 

 Closely above the position of the cross are the first barb-like 

 spines, of which there are usually two opposite each other, or 

 sometimes more than two in a whorl. The rest of the spines are 

 arranged along the shaft in an approximately regular spiral row. 

 The bundles of basal spicules, so long as they run alongside 

 the skeletal tube, are as a rule entirely covered by the flake- 

 tissues — not exposed by the falling off of the latter. Superiorly 

 they extend in the wall for fully two-thirds of the body-length. 



The dermalia (PI. IV, figs. 16, 28 ; PI. V, fig. 36)— sword-like 

 hexactins as usual — have rays which are on an average 10 o- thick 

 near the center and taper out to more or less sharply pointed 

 ends. In certidn specimens, however, the hilt-ray was often 

 bluntly rounded at the end, but never showing a swelling in its 

 course. The length of the hilt-ray is 130-170//, on an average 

 150 (x ; blade-ray generally more than 3 times as long, up to 

 700/^; guard-rays somewhat longer than the hilt-ray. These 

 form the well-known dermal latticework, the meshes of which 

 are about 200/^- in width. Both the hilt and the blade rays 

 possess for the greater part of their length sparingly distributed, 

 minute tubercles. The guard-rays are nearly quite smooth all over. 



A specially large size is attained by those dermalia which 

 are situated along the free edge of the cuff and of certain parietal 

 crests and whose hilt- ray stands in association with the prostal 

 oxydiactins already described. These dermalia are frequently 

 nearly 2 mm. long, the hilt-ray measuring 300-400/^ in length. 

 The rays may be twice as thick as in the ordinary dermalia of 

 the general surface, 



