A REVISION OF THK GENUS STEGANOPORELLA. 243 



at the commencement of the descending portion. Tube well 

 developed, rising very asymmetrically from the descending 

 cryptocyst; its opening vertical, completed by the basal 

 wall, or if complete not far raised above the basal wall. The 

 formation of a median process distinct from the tube is 

 indicated only by a pair of unequally developed horns on the 

 upper wall of the tube, b opercula rare, with fl-shaped main 

 sclerite, but without basal sclerite ; submarginal teeth long, 

 strong, and recurved, confined to the distal half of the 

 operculum, a opercula undifferentiated. Insertion of the 

 cryptocyst, as shown on the back of the zooecium, usually 

 produced proximally into a deep asymmetrical sinus 

 (fig. 27). 



(a) Tahiti; Manchester Mus., Miss E. C. Jelly.^ 



(6) Tahiti; Hincks Coll., Brit. Mus., 99.5.1, 261 [from 

 Miss Jelly's collection] . 



(c) Torres Straits ; Haddon Coll., Cambridge Mus., 24.2.98 

 [Muddy Creek, Victoria (Tertiary), MacGillivray]. 



The material on which the diagnosis is based consists of 

 three small encrusting specimens, two of which, from Miss 

 Jelly's collection, were no doubt obtained at the same time. 

 The specimen from Toi'res Straits is without opercula. 



Of all the species I have examined this one most nearly 

 resembles a Siphonoporella, and I have accordingly put it 

 at the head of my list. The tube (fig. 1) arises quite asym- 

 metrically from the cryptocyst, as pointed out by MacGil- 

 livray, sometimes from one side, sometimes from the other, 

 and its position in a series of zocecia does not obey any 

 obvious law. The change from a right-handed to a left- 

 handed zooecium takes place abruptly in the course of a 



ing of the operculum or epitheca, following a practice usual in entomology. 

 The "main sclerite" is the principal thickening bar of an operculum, which 

 bears the tubercle for the insertion of the occlusor tendon. 



1 The localities given are those of the specimens which I have myself exa- 

 mined. The specimen first mentioned is the one which I regard as the type- 

 specimen in the case of the new species. In the remaining species "B. M." 

 = British Museum, " C. M." = Cambridge Museum, the register dates being 

 given in both cases. 



