246 STDNKY F. HAIiMER. 



tion from above. The free edge d is in most species some- 

 what thickened, so that the first impression, in examining a 

 transparent preparation, is that the main sclerite bifurcates 

 proximally into two limbs, one of which is really the base 

 line of the sclerite, the other its free edge. The intermediate 

 oblique portion of the sclerite may be so thin as to appear to 

 be a foramen ; but in some cases at least I have satisfied 

 myself that the apparent foramen is merely a thin part of 

 the sclerite. 



A feature of the b operculum of S. lateralis, to which 

 attention must specially be directed, is the absence of a 

 basal sclerite, this being indeed the only species in which I 

 have found this condition to occur in the b opercula. 



The general structure of the a opercula (fig. 19) is very 

 similar to that of the b form. The differences are — its 

 smaller size and greater relative breadth ; the absence of 

 teeth ; and the somewhat more distal position of the occlusor 

 tubercle. As this type of operculum does not appear to differ 

 widely from those of other Cheilostomes, I describe it in the 

 present paper as " undifferentiated." 



The diameter of the b opercula is about 515 fx, and that 

 of the A opercula about 415 yu. 



2. S. sulcata, n. sp. Figs. 2, 14—17, 28, 29. 



Steganoporella magnilabris, Hincks, 'Ann. Nat. Hist.' 

 (5), xiii, 1884, p. 358; ' Journ. Linn. Soc.,' xxi, 1889, 

 p. 130. 



Cryptocyst joining the basal wall, angulated and thickened 

 at the commencement of the descending portion. Tube 

 short, its opening vertical and completely separated from the 

 basal wall. Median process variable, usually broad and with 

 a shallow cavity, the deepest part of which is a median lon- 

 gitudinal groove (hence sulcata) ; or narrow and y-shaped. 

 b opercula rare, with D -shaped main sclerite; submarginal 

 teeth well developed, sometimes long and weak, confined to 



