176 CEYLON PEARL OYSTER REPORT. 



B. studeri, Whitelegge, B. philippi, Studer, and B. hicksoni already described by 

 us (Part III., p. 294). In our account of B. hicksoni we referred to what might be 

 regarded as varieties of that species, but some additional specimens which we have 

 studied cannot so be dealt with. 



All are dark-coloured irregularly branched colonies, disguised by a growth of 

 monaxonial siliceous sponge, and with one exception spreading in one plane. The 

 exception has seven alternate branches, terminally clavate, on an average 2 millims. 

 in diameter, and is 8 centims. in height by the same in maximum breadth. One of 

 the specimens attained a height of 1 8 centims. 



The verrucse are prominent truncated cones, usually on all sides of the main stem 

 and branches, but sometimes almost restricted to the sides in the plane of branching. 

 They are about 1 - 5 millims. in height and breadth, and are separated along one line 

 by intervals of 1*5 millims to 2 millims. Except in a few cases, the polyps are 

 completely retracted and the verrucae are thickly beset with sponge spicules. 



The axis is non-calcareous, light brown in colour, very soft and flexible, and 

 traversed by twisted longitudinal grooves whose depth has doubtless been increased 

 by shrinkage of the core. The diameter of the axis is about T25 millims. 



When the sponge spicules are carefully removed, the surface of the ccenenchyma 

 exhibits the characteristic Bebryce appearance. There is a coherent mosaic of 

 interlocked tuberculate discs, and large pieces can be separated off after slight heating 

 without any loosening of the component spicules. The average thickness of the 

 ccenenchyma is about 0"3 millim. 



On the few polyps which could be satisfactorily seen, there were relatively large 

 tuberculate spindles. 



The following types of spicules occur : 



(a) Almost regular tuberculate quadriradiate forms, with more or less pronounced 

 cruciate arms, and sometimes at least with an internal boss at right angles to the 

 expanded disc, O'l 5 millim. x O'l 25 millim. in length and breadth of the disc. 



(b) Irregular quadriradiate forms, with the arms to one side longer and stronger 

 than those to the other side; - 25 millim. between the tips of the longest arms, 

 0"15 millim. between a long and a short arm, O'l millim. between the two short arms. 



(c) Approximately square forms, suggestive of amphiccelous vertebrae, with slightly 

 prolonged corners and slightly concave sides, 0'175 millim. x 0'175 millim. ; and 

 transitional forms connecting these with the pronounced quadriradiate types. 



(d) Tuberculate "capstans," with a very slightly marked middle zone, separating 

 two equal portions; and a variety of this "double-club" type with the part to one 

 side of the waist much smaller than the other a feature prominent in the spicules of 

 some other species of this genus ; 0'125 millim. x O'l millim. in height and breadth. 



(e) Small tuberculate forms, more like " double wheels" than capstans ; O'l millim. 

 x O'l millim. in length and breadth, and 0'04 millim. across the " waist." 



(/) Bent, warty spindles from the polyps, including (1) short, thin, rough forms 



