A REVISION OF THE GENUS STEGANOPORELLA. 245 



across the zooecium, along the line where the descent of the 

 cryptocyst commences. The descending portion joins the 

 horizontal portion at a distinct angle^ and the tube springs 

 from it at a deeper level than the tubercular edge. As is 

 usual in species in which the cryptocyst descends verti- 

 cally, the basal wall is well exposed from above. The oral 

 shelf is completely absent. The oi'al arch is well raised. 

 The epithecal sclerites are rather long, nearly straight 

 proximally, curving outwards distally towards the ends of 

 the main sclerite of the operculum, which they nearly reach. 

 The epitheca is delicate and transparent. 



The characters of the b zooecia have not been observed ; 

 but two B opercula have been found with respectively ten 

 (fig. 20) and nine submarginal teeth, but otherwise closely 

 agreeing with one another. The tendons of the occlusor 

 muscles are shown in the sketch, that on the right side being 

 displaced from its natural position. They are inserted, as 

 in the case of the opercula of Steganoporella generally, 

 into a distinct tubercle (a), which is marked by a group of 

 fine dots which doubtless correspond with a fibrillar insertion 

 of the tendon into the operculum. The main sclerite (b c) 

 of the operculum is H-shaped; and, as seen from the inner 

 or basal side, is an oblique girder springing from the oper- 

 culum along the line c, and with a free edge at b. This edge 

 rises further from the plane of the operculum on the proxi- 

 mal side of the occlusor tubercle, and projects as a pointed 

 lobe whose edges are formed by the parts d and e, between 

 which there is a deep concavity sinking down to the level 

 of the proximal end of the base-line (c) of the sclerite. 

 This upstanding lobe is supported by a buttress or sclerite 

 (/), which passes down to the plane of the operculum. The 

 line c, the buttress /, and (in some cases) the submarginal 

 tooth-bearing sclerite, being the parts which are most in the 

 plane of the operculum, are conspicuous as dark lines on the 

 opercula in an ordinary dry preparation seen from above. In 

 the present species, which is characterised by the delicacy of 

 its opercula, the lines c and ^ can be seen in a dry prepara- 



