A HE VISION OF THFl GRNUS STEOANOPORELLA. 247 



the distal half of the operculum^ which has a distinct basal 

 sclerite. a opercnla with two strong teeth on the distal 

 part of the main sclerite ; the teeth sometimes vestigial. 

 Back of the zooecium showing the insertion of the cryptocyst, 

 distal to which the basal wall is commonly thin, so as to form 

 a rounded fenestra, through which the tube is visible. 



{a) Isle des Neufs, Arairante Is,, Indian Ocean, Voy. 

 " Alert,^' 15 fathoms (B. M., 82.10.18, 88). 



{b) Darros I. (Amirante Is.), Voy. " Alert," 22 fathoms 

 (B. M, 82.10.18, 125). 



(c) Galle Point, Ceylon, Dr. Ondaatje (B. M., 85.7.27, I). 



{d) Mergui, Burmah, Hincks Coll. (B. M., 99.5.1, 28). 



(e) Mergui, Burmah, Dr. Anderson (B. M., 85.12.29, 10). 



(/) [Possibly N. Australia.] "On Avicula margari- 

 tifera" (B.M.). 



All the specimens are encrusting. The largest, from 

 Darros Island, encrusts the greater part of a cylindrical piece 

 of coral limestone, about 85 x 30 mm. The existence of the 

 specimen (d) in the British Museum collection enables me to 

 state that " S. magnilabris" recorded by Hincks from the 

 Mergui Archipelago belongs to this species. 



S. sulcata appears to be closely allied to S. lateralis, 

 from which, however, the characters of the tube ai*e sufficient 

 to discriminate it. The opening of the tube is circular and 

 complete, and it is often well separated by a portion of the 

 descending cryptocyst from the basal wall, a large part of 

 Avhich is visible from above. A median vertical calcareous 

 wall usually rises from the roof of the tube, and tyjjically 

 diverges above into the two flanges which are seen to unite 

 in the median groove (fig. 2) which is one of the most strik- 

 ing features of the species. A transverse section through 

 the tube and its annexes could accordingly be represented 

 by a circle on which is standing a short-legged Y with very 

 divergent arms. On the analogy of S. alveolata (see p. 229) 

 it may be confidently stated that the tentacle- sheath passes 

 through the opening of the tube round the distal end of the 

 median process. The transverse distal border of the latter is 



VOL. 43, PART 2. NEW SERIES. S 



