HEXACTINELLA. 143 



transverse beams, whieh, to a certain extent, also form skeleton-net lamellae. 

 These transverse lamellae are, however, not nearly so compact and so regularl}^ 

 arranged as the longitudinal ones. Together the longitudinal and the transverse 

 skeleton-net lamellae form a network with meshes about 0.7 nnn. broad and 

 0.7-1.5 mm. long. 



The skeleton-net lamellae of the outer zone, that is the one bordering on the 

 convex side (Plate 32, fig. 8), are composed of a network of beams mostly 450- 

 650 ij. thick, which enclose roundish irregular meshes, usually 1.5-2.5 mm. wide. 

 The beams of this network are covered with large, rounded protuberances. Its 

 meshes are either ciuite empty or contain only slight traces of a fine secondary 

 network, similar to that in the inner zone, described below. The skeleton-net 

 lamellae of the inner zone, that is those bordering on the concave side (Plate 32, 

 fig. 9), are composed of a primary network in the meshes of which a fine secondary 

 network is spread out. The primary network consists of smooth, longitudinal, 

 transverse, and oblique beams. The longitudinal beams are situated either 

 singly or in bundles of two or thi-ee. Those of the same bundle are connected 

 at frequent intervals by short transverse beams. Here and there they even 

 coalesce to form irregular stems sometimes 350 ix thick. The individual longi- 

 tudinal beams are usually about 130 ^ thick, the transverse and oblique 60-110 yn- 

 The meshes are very irregular and are sometimes more than 1 mm. long. Thorns 

 about 200 fi long, 40 /i thick at the base, and provided with low, rounded protu- 

 berances arise from some of the nodes of this network. The secondary network 

 extends in the meshes of the primary and in the transverse band above referred 

 to, and also occupies the interstices between the lamellae. It is composed of 

 ])eams, 5-10 m thick, which enclose square, rectangular, or, more rarely, irregular 

 meshes 50-130 ^ wide. 



TRETOCALYCIDAE F. E. Schulze. 



Hexasterophora with ramified afferent and efferent canals. With a firm 

 reticulate supporting skeleton and uncinates and generally also scopules. 



The collection contains one specimen and three fragments of this family, 

 which belong to Hexactinella. 



HEXACTINELLA Carter. 



Tretocalycidae which are calyculate or composed of simple, ramified, or 

 anastomosing tubes; with firm reticulate supporting skeleton, uncinates, scopules, 



