306 CEYLON PEARL OYSTER REPORT. 



The fragment comprises twenty-two setigerous segments, total length about 

 30 millims. ; width of thoracic region 3 to 4 millims. ; thorax straight, porrect, 

 abdominal region bent, with smooth, convex, turgid dorsum. The pharetrse setarum 

 are high, upwards of 1 millim. in front, decreasing gradually backwards. The simple, 

 narrowly limbate setae issue in two principal bundles from between the oblique lips. 

 The ventral portions of eleven segments from the second are flattened, forming bi'oad 

 ventral shields subdivided by transverse grooves. There are nine torigerous segments 

 in the thoracic region, the posterior thoracic segments being nearly as long as broad. 

 The thoracic tori graduate insensibly into the abdominal tori, which are sessile, not 

 pinnuliform. The uncini have the form shown in Plate VII., fig. 165, and the general 

 formula 1-22-3. In side view the three tiers of teeth show clearly. 



The branchial filaments are numerous, forming dense coils. Those of the first 

 acervus commence low down near the ventral surface. They break away easily from 

 the body in groups. The tentacular cirri, plainly grooved on the lower side, are much 

 stouter than the branchial filaments (Plate VII., fig. 164). The three branchiferous 

 segments also carry capillary fascicles, the first uncinigerous torus occurring on the 

 first post-branchial segment. The branchiae arise from the anterior parts of the 

 segments in front of the corresponding capillary fascicles. 



Family: SABELLID^E. 

 Branchiomma acrophthalmos, Grube Plate VII., figs. 166 and 167. 



This is the oriental form of the well-known B. vesiculosum. 



Locality : East Cheval Paar, Gulf of Manaar. 



Baron de St. Joseph has shown that the character of the limbate setae of the 

 European species varies at different ages, being spatulate in the young. 



The Ceylon specimen is a fragment comprising 16 segments, 21 millims. long 

 (including the gills), 3 millims. wide; 15 radioles* in each gill; gills banded about 

 six times purple and whitish. Each radiole carries a subterminal eye, the two dorsal 

 eyes being the largest. The definition of Branchiomma given by de St. Joseph 

 (1894, 'Ann. Sci. Nat.,' xvii., p. 249) states " Soies dorsales d'une seule sorte au 

 thorax." In the Ceylon specimen the dorsal fascicles of the thorax appear to contain, 

 and in fact do contain, two distinct kinds of setse, normal limbate to the number of 

 eleven, and spatulate (Plate VII., fig. 166) to the number of nineteen. The thoracic 

 tori are biserial, containing a row of avicular uncini and a row of cuspidate setae. 



Grube describes ('Ann. Semp.,' 1878, p. 258) the collar as trilobate, apparently 

 overlooking the ventral incisure which divides the two acuminate ventral lobes. 

 These are in close juxtaposition and give the appearance of the simple wide triangular 

 lobe described by Grube. The dorsal portions of the collar show a characteristic 

 form, the free border deeply emarginate externally and reflected round the base of 

 the gill-supports (Plate VII., fig. 167). There are eight thoracic segments. 



* See definition of this term on p. 308. 



