250 CEYLON PEARL OYSTER REPORT. 



which may owe its existence to the disintegration of algae cells, so abundant in many 

 tropical corals (see below). 



The Spicule.s are long and slender, and in form are characteristic of the genus 

 (fig. 2). They are smaller in the actively growing superficial tissues than elsewhere. 

 When an autozooid is in a state of contraction, the external aperture is effectually 

 closed by a small conical cap of minute tentacular spicules. 



This species exhibits considerable variation in form and consistency, but is charac- 

 terised externally by the distinctive creamy white autozooids and siphonozooids and 

 the greyness of the remaining portions of the colony. 



Sarcophytum oligotrema, n. sp. Plate I., figs. 3 to 5. 



A complete cup-shaped colony attached basally to stony coral was taken in the 

 Gulf of Manaar (fig. 3). 



The specimen is almost stalkless and is 42 millims. high. The capitular cup, 

 irregular in outline, is 32 millims. in depth and is 62 millims. by 50 millims. in 

 breadth. The base of the cup is 10 millims. in thickness, the sides are about 

 5 millims. in diameter near the base, but thin out towards the edge, so that they are 

 wedge-shaped in vertical section. Zooids are only present on the inner surface of the 

 cup. The colour in spirit is of a dirty brownish-grey, with autozooids of a more 

 pronounced brownish hue. The outer surface of the cup is moderately smooth, with 

 few wrinkles. The specimen is moderately hard and tough. 



Autozooids are very small, and are relatively very numerous on the sides and edges 

 of the cup, but are somewhat scanty in the middle. As the colony is in a state of 

 extreme contraction, it is impossible to determine the actual size of the autozooids ; 

 the young autozooids near the edge of the cup are smaller than elsewhere. The 

 average diameter of a mature autozooid at the surface is about 0'3 millim. 



The tentacles, stomodteum, mesenteries and mesenterial filaments do not differ in 

 any essential respect from those of other species. Reproductive organs were not 

 observed. 



Siphonozooids are remarkably few in number (fig. 4). Usually only one or two 

 of these zooids occur between two autozooids, but in the middle of the capitulum 

 the number is slightly increased. The average superficial diameter of a siphonozooid 

 is 0'35 millim., the mouth is sunk in a slight depression, and the stomodseum has an 

 average length of 0'25 millim. 



The canal system presents no specially interesting features. Transverse ciliated 

 vessels connecting the coalentera of neighbouring zooids (PRATT, 1903, p. 507, fig. 3) 

 are very numerous. 



The spicules, in the form of irregular warted spindles, are extremely small, but are 

 characteristic of the genus. They are from 0'09 millim. to 0'3 millim. in length and 

 from 0'09 millim. to O'l millim. in diameter (fig. 5). 



This species has a superficial resemblance to S. roseum, from which however it 



