REPORT ON THE HEXACTINELLIDA. 163 



shaped terminally, but simply rouuded, or else with a Ijlunt point (PI. LXI. fig. 9). The 

 node of intersection is frequently thickened, and usually exhibits a slightly projecting 

 tubercle, representing the undeveloped sixth ray. While this sixth ray is undeveloped 

 in the gastraLia proper, it appears distinctly on the spicules which serve to support the 

 lining of the efferent canals, and exactly resembles the other five rays. The canalaria 

 are therefore oxyhexacts, and the sixth ray usually projects for a greater or less distance 

 into the lumen of the efferent canals. While they form a continuous layer on the internal 

 surface of the wider canals, they occur more sparsely in the narrower branches, and may 

 finally be altogether absent (PI. LXI. fig. 3). There are no special marginalia, since the 

 lamellar oscular fringe described above ends in a simple smooth edge. 



The stalk demands special notice. Though its structure essentially resembles that of 

 the cup-shaped body, there are several peculiarities worth noting. It is penetrated by 

 several anastomosing longitudinal canals which open above into the gastral cavity of 

 the cup, and receive laterally the short efferent canals of the wall. 



The long diacts of the parenchyma have almost exclusively a longitudinal disposition, 

 and are more or less abundantly and firmly united by transverse synapticula, so that the 

 whole stalk, being penetrated and supported by a continuous and connected framework, 

 is very compact and firm. Only near the external surface, and near the upper end where 

 the stalk joins the cup, are the parenchymal spicules united to a less extent, or not at 

 all. Between the diacts there is a comparatively abundant occurrence of small thick 

 hexacts, which may be isolated, but generally have one or two opposite rays laterally 

 united by a siliceous mass to the long diacts (PI. LXI. figs. 5, 6). 



The degree of amalgamation and connection by means of synapticula increases from 

 above downwards, so that the basal enlargement is traversed by a dense and stony siliceous 

 framework. 



The oxyhexasters which occur so abundantly in the parenchyma of the cup-shaped 

 body are less frequent in the stalk, and are only found in those portions where the union 

 of the spicules by amalgamation or by synapticula has not occurred to a very marked 

 extent. I have observed that small discohexasters only occur isolated. 



The skeleton of the smooth external skin-layer exhibits medium-sized hy|)odermal 

 pentacts and small rough dermal pentacts or tetracts, with rounded or slightly club- 

 shaped ray- tips, like those which occurred in the dermal skeleton of the cup-shaped body. 



On the inner surface of the large longitudinal efferent canals of the stalk, similar 

 roughened pentacts also occur, with rounded or slightly club-shaped ray-tips. These 

 correspond to the pentact gastralia of the gastral cavity in the superior cup-shaped 

 portion. 



This form, which Bowerbank received in 1877 from Dr. A. B. Meyer, and described 

 as an anomalous Hyalonema,^ is not a Hyalonema, but certainly Crateromorpha 



1 Proc. Zool. Soc. Land., p. 461, 1877. 



