A REVISION OP THE GENUS STEGANOPORELLA. 2 75 



oi' distal wall, on the contrary, shows two curved obliquely 

 horizontal lines (fig. 33) corresponding with the insertion of 

 the floors of the two lateral recesses. 



The epithecal sclerites are short, uearl}- straight, distant 

 from one another, and not nearly i-eaching the operculum. 



The B opercula (fig. 34) have about thirty submarginal 

 teeth. The series begins not far from the base of the oper- 

 cukmi, and the teeth are short and small, or even vestigial. 

 The submarginal sclerite is not sharply defined, and the 

 parallel part of the main sclerite projects but little above the 

 general level of the operculum. On the proximal region of 

 this part the halves of the main sclerite diverge so as to form 

 a bold arch, which is completed distall}^ by the edge of the 

 chitinous portion which connects the two parallel parts of 

 the bar. The projecting proximal ends of the sclerite are 

 less everted than those of S. haddoni. The basal and 

 oblique sclerites are well developed. The a opercula (fig. 35) 

 are of the '' undifferentiated " type. 



This species is a somewhat variable one. The Fort Eliza- 

 beth specimens (a) are bilaminar, while that from North 

 Celebes {d) is encrusting. The zocecia of the South African 

 forms (ft, b) are larger than those from other localities, and 

 their opercula are more robust. There is considerable varia- 

 tion in the form of the opercula. The R form shown in fig. 34 

 may be regarded as a long one, as it is considerably longer 

 than broad ; others, even of the same colony, being relatively 

 much shorter and even a good deal broader than long. In 

 these cases the parallel portion of the main sclerite is shorter 

 than in fig. 34. The specimen (e) from Torres Straits has 

 conspicuously short and broad b opercula. 



The diameter of the opercula (in /x) is as follows : 



