I 1 4 CEYLON PEARL OYSTER REPORT. 



in Mr. Carter's collection (now in my possession), the rays of the chiasters are 

 occasionally tylote, though not nearly so strongly as in the Ceylon specimens.* 

 R.N. 199, 200 (Stat, LXVIL, off Talaivillu Paar, 10 to 14 fath., Gulf of Manaar). 



Tethya lyncurium, Lin., var. h. 



There are five specimens in the collection which may be referred to this variety, 

 differing from the foregoing in the following respects : 



(1) There are no prominent vents. 



(2) The surface is more or less distinctly tessellated. 



(3) The spherasters are considerably larger and more numerous, and have more 

 numerous rays and larger centra. Total diameter up to about O'l millim., with rays 

 about 0'024 millim. long; sometimes they are a little smaller; usually they are 

 densely crowded in the cortex ; the number of rays appears to be usually about 25. 



(4) The chiasters are more distinctly differentiated into two kinds, the rays of 

 those of the choanosome showing a strong tendency to lose their tylote character and 

 become strongylote or even oxeote, while at the same time elongating somewhat (but 

 not much) and being (? always) slightly roughened. 



The largest of the five specimens is only about 21 millims. in diameter. The colour 

 in spirit is dull grey. 



R.N. 180, 180a, 180b (all from Lagoon, Galle) ; 196 ; 211 (Gulf of Manaar). 



Tethya lyncurium, Lin., var. c. 



This variety is represented by a single specimen, about 24 millims. in maximum 

 diameter, with very strongly tessellated surface and one prominent vent. The cortex 

 is very lacunar between the polygonal, flattened tesserae. 



As regards spiculation, this variety differs from the preceding only in the presence 

 of numerous well-developed oxyasters, chiefly in the choanosome. These spicules 

 have little or no centrum and usually six rays. The rays are rather slender and 

 sharp-pointed, sometimes slightly roughened, but very rarely spined or branched ; 

 usually straight or nearly so. Total diameter of the oxyaster about 0'04 millim. 



This variety might be justifiably identified either with Selenka's Tethya maza or 

 with Percival Wright's T. seychellensis, but the two preceding varieties unite it so 

 closely with T. lyncurium that it seems to me quite unnecessary to make a specific 

 distinction. 



R.N. 19 (Gulf of Manaar). 



The occurrence of these three varieties of Tethya lyitcurium within the same limited 

 area is a very interesting fact, and their discovery is likely to be of great assistance 

 in elucidating the relationship of the so-called species of this extremely difficult genus. 

 In this connection it is interesting to note that Wilson (29) has lately recorded the 

 occurrence of both T. lyncurium and T. seychellensis in Porto Rico. 



' Topsent, however, entertains (14) a different view ;is to the taxonomic value of the tylote character, 



