308 CEYLON PEARL OYSTER REPORT. 



Dorsal Tubercle a simple horse-shoe, with the opening on one side (fig. 21). 



Locality : Station LTIL, 10 miles north of Cheval Paar, 9 fathoms. 



This little Molgulid is externally very similar to the Polycarpa (P. decipiens), the 

 Styela (S. lapidosa), and the Rhabdocynthia (Rh. ceylonica), with which it is found. 



I have named this species after Sir West Ridgeway, who was Governor of Ceylon 

 at the time when it was collected. 



Family: CYNTHIID^. 



Notwithstanding Michaelsen's remarks (' Zool. Jahrb.,' Suppl. viii., 1905, p. 79), 

 and the fact that several recent writers have seen fit to relinquish the genus 

 Rhabdocynthia, I believe it is both useful and natural to group together those species 

 of "Cynthia" that show echinated unbranched calcareous rods or spindles in the 

 connective tissue of the body. The grouping of species into genera is largely a matter 

 of convenience, and if a set of closely related species can be defined and recognised by 

 the possession of a common character, the application of a generic name seems 

 justifiable, and is certainly an aid in classification. On these grounds I make use of 

 Rhabdocynthia as the generic designation of the set of species which may be grouped 

 around Heller's Cynthia pallida. 



Rhabdocynthia pallida (Heller) Plate II., figs. 36 to 39. 



The shape is irregularly ovate or pyriform, the anterior end being rather the wider. 

 It is attached by the posterior end and a part of either side, and the lower half may 

 be more or less encrusted with sand and shell fragments. The four-lobed apertures 

 are both anterior, placed on long siphons, moderately far apart and turned away from 

 one another (fig. 36). The colour in the preserved specimens is dull milky white, 

 becoming pale yellow in places ; it was of a reddish tint when alive, and traces of pink 

 are still to be seen in some specimens, esjjecially at the branchial and atrial siphons. 



The Test is of a soft leathery texture, much wrinkled on the outer surface, smooth 

 and glistening on the inner and white in section. It is mostly from 1 to 3 millims. in 

 thickness, but may be thickened at the posterior end up to nearly 3 centims. 



The Mantle is rather thin and weak over the viscera, soft but opaque and muscular 

 on the anterior half of the body and very muscular on the siphons (fig. 37). It 

 bristles with minute calcareous spicules in all parts, which renders it rather easily 

 torn, and very unpleasant to manipulate. 



The Branchial Sac has nine wide folds on each side. They converge to the 

 oesophageal opening. 



The Dorsal Lamina is represented by a series of about 20 short curved pointed 

 tentacular languets. 



The Tentacles are of three sizes. There are about eight large and much branched, 

 alternating with others half the size, while a variable number of much smaller ones 

 occur between. If a little more regular the formula would be eight large, eight 



