m 8 CEYLON PEARL OYSTER REPORT. 



It is not easy to define the limits of the genera Pomatoceros, Phtlippi (1844) and 

 Spirobranchus, Blainville (1818). Grube uses Pomatoceros in an extended sense 

 and appears to disregard the prior claims of Spirobranclius ; the latter is retained by 

 Ehlee*s (1887) and St. Joseph (1894). The genus Pomatoceros s. str. comprises the 

 species crucigera, Grube (Ked Sea, 1869), helicoides, Marenzeller (Japan, 1884), 

 triqueter, L. (Europe, Morch, 1863, St. Joseph, 1894), and bucephalus, Morch 

 (Philippines, 1863). Grube's Serpula quadricornis ('Ann. Semp.,' p. 275) appears 

 to me to be probably co-specific with Morch's Spirobranchus semperi (' Kevisio 

 Serpulidarum,' 1863, p. 405). The species of Pomatoceros named above practically 

 resolve themselves into two main groups represented respectively by the European 

 P. triqueter and the Oriental P. bucephalus. 



Spirobranclius semperi, Morch. 



Morch, 'Revisio Serpulidarum,' Copenhagen, 1863, p. 405. 

 Serpula quadricornis, Grube, 'Ann. Semp.,' 1878, p. 275. 



Opercular style with wing-like expansions as in the preceding species, opercular 

 disc flat, carrying four distinct horns. Uncini from the last thoracic torus with 

 12 to 13 teeth. 



Spirobranchus semperi, var. acroceros, no v. Plate VII., fig. 193. 



This variety is represented by several specimens apparently only differing from the 

 typical form in the fact that the opercular disc is cone-shaped, carrying the horns at 

 the top (Plate VII., fig. 193). Length 12 - 5 millims. (up to nearly 20 millims.) ; about 

 50 abdominal segments ; gill with 1 8 radioles. 



Spirobranchus tricornigerus (Grube). 



Serpula tricornigera, Grube, 'Ann. Semp.,' 1878, p. 273. 

 A small specimen from the pearl banks. The great feature of this species is the 

 horizontal branching of the horns of the operculum, the main branches very slightly 

 elevated and the ultimate ramifications lying approximately in one plane. The horns 

 are very pale, calcareous, slightly chitinised. It is possible to distinguish three main 

 branches proceeding from a common centre, but not so equilateral as in Grube's 

 figure. Grube assigns 20 teeth to the larger thoracic uncini. I only see the usual 

 1 2 teeth in the uncini of the last thoracic torus. The buccal setae forming the first 

 thoracic fascicle are of two kinds, simple capillary and bayonet setae, both kinds with 

 serrulate border. The gills are traversed by a strong, nearly black fascia a short 

 distance in front of the basal membrane. 



Vermilia pygidialis, n. sp. Plate VII., figs. 194 to 196. 



Locality : South-west Cheval Paar. 



Distinguished by the long, brown, horny, ringed, conoidal operculum, and by the 

 obtuse posterior end of the body, which is furnished dorsally with an oval purplish- 



