298 CEYLON PEARL OYSTER REPORT. 



principal plane of branching. The branching is very profuse and at several points 

 shows anastomosis of the branches, but this is by no means common. The branches 

 are cylindrical, but there are traces of slight flattening in the plane of branching. 

 The twigs arise usually at right angles to the branches, and their tips as well as those 

 of the branches are slightly clavate. 



The polyps are small and are scattered over the whole surface of the stem and 

 branches. In no place can it be said that they are confined to three surfaces, nor can 

 any attempt at lateral arrangement be seen. The verrucse are very small and the 

 polyps can be completely retracted within them. The edges of the verrucae show a 

 variable number of spines which project above the slightly conical operculum formed 

 by the tentacular spicules when the polyps are withdrawn. 



The superficial coenenchyma of the stem and the branches presents a striking 

 appearance, due to the arrangement of the large flat whitish spicules and to their 

 being outlined against the darker ground-colour of the stem and branches. 



The spicules of the general coenenchyma are flat and multituberculate, varying very 

 much in size and shape. The tubercles are low and rough and very numerous. 

 Many of the larger spicules extend the whole distance between two adjacent polyps, 

 and sometimes even exceed this length. They fall into three groups, fairly distinct 

 in shape : (a) large modified fusiform spicules, which taper more or less towards the 

 ends and measure from 0'9 millim. to 3 millims. in length by 0'25 millim. to 

 0'45 millim. in breadth ; (b) squamous or scale-like spicules, often with slightly lobed 

 margins, which measure from 0'8 millim. to I'l millims. in length by 0'4 millim. to 

 0'6 millim. in breadth ; and (c) large modified squamous spicules, consisting of a 

 flattened tuberculate basal portion and of a projecting part which forms the projecting 

 spine of the verrucse. They measure, in length by breadth in millimetres, as 

 follows: 07 X 0'5; 0'6 X 0'4 ; 0'5 X 0'3. 



In the polyps there are slender spindle-shaped and club-shaped spicules. They are 

 often slightly curved and either taper to both ends or are blunt and rounded at one 

 end and pointed at the other. Many of these exhibit fairly prominent spines towards 

 the thicker end. They vary considerably in size, being from 0'3 millim. to 0'5 millim. 

 in length and from 0'02 millim. to 0'06 millim. in breadth. They are found chiefly in 

 the tentacles, where they form an operculum to the retracted polyp ; but an 

 incomplete and irregular crown or collar is formed by them at the base of the 

 tentacles. 



In colour the spicules vary from white to semitransparent, while the whole colony 

 has a whitish-brown appearance. 



This species differs from Acis pustulata in not having violet-coloured opercular 

 spicules and in the branches not being compressed in the plane of branching. It also 

 differs from Acis oriental/if in having the polyps on all sides of the stem and branches 

 and in the branching not being confined to one plane. 



Locality : Deep water off Galle. 



