234 



arise mostly at right angles, but after a more or less sinuous course run sub- 

 parallel to the main stem. The specimen is paler in colour than the type and 

 the spicules are almost visible to the naked eye. In other respects the colony 

 agrees with the description given in the " Ceylon Pearl Oyster Fisheries Report ". 

 Locality : Andamans. 



Acis pustulata, Wright and Studer. 

 Plate I. figs. 6 and 7 ; Plate IX. figs. 5a, .5b. 



There is in the collection a magnificent, upright, robust colony 22 cm. high 

 and 25 cm. in maximum breadth. It is densely branched in one plane forming 

 an almost felt-like fan-shaped mass. It has been attached to a rock by a 

 claviform base PS cm. in diameter and 15 cm. in height. The main stem 

 measures (3 mm. in diameter near the base, it ascends to the top of the colony 

 where it diminishes to 1 mm., equal in thickness to the smaller twigs. 



It is very sinuous, diverging at a distinct angle at the origin of all the 

 larger branches, and this is also a characteristic of the branches themselves. 

 It gives off" three large branches, the first at 2'5 cm., the second at 3"8 cm., and the 

 third at 5 cm. from the base. The average diameter of these branches is -t mm. 

 Two ascend to the top of the colony but the third is broken. They also give off 

 large sinuous branches, which, however, are few in number, and have an average 

 diameter of 3 mm. Innumerable small twig-bearing branches arise from the 

 main stem and larger branches and diverge in all directions, forming an intricate 

 maze. These vary in thickness from P5 mm. to 1 mm. and seldom overlap. 



The two sides of the colony are quite distinct in appearance, the dorsal 

 being almost white, the ventral, polyp-bearing surface presenting a dotted 

 structure due to the brown polyps which stand out in relief from the otherwise 

 monotonous background. 



The coenenchyma is thin on the main stem and is com])osed of a single 

 layer of scale-like plates very irregular in outline. They conform in shape to 

 the adjacent spicules but do not fit closely, so that each individual spicule can 

 be distinctly seen with the naked eye although much more minute than on the 

 younger portions. The genei'al appearance is that of an irregularly tessellated 

 pavement with somewhat circular tiles. In the upper part of the colony larger 

 and more rectangular plates ajjpear sparsely scattered over this fundamental 

 layer. On the smaller branches, quadrangular and elongated diamond-shaped 

 forms predominate, but there is also an inner layer of small rough spindles. 

 The circular forms again appear in greater abundance on the twigs where the 

 coenenchyma is much thicker and the scales more irregular. On the verrucse 

 two types of arrangement seem equally frequent. In the first type there 

 is the same tessellated structure as in the coenenchyma, but in the second 



