A REVISION OF THE GENUS STEGANOPOBELLA. 287 



12. S. alveolata, u. sp. Figs. 12, 32, 40, 41. 



A and B zooecia of about equal size, a extremely rare ; both 

 forms shortly obloug with angles hardly rounded, the oral 

 arch hardly distinguishable. Cryptocyst descending steeply, 

 without angulation ; in B inserted at or near the junction of 

 the basal and distal walls, in a meeting the basal wall at a 

 great distance from the distal wall. Median process with 

 very deep cavity, the roof of the tube forming its floor ; with 

 rounded, often everted border in b, appearing transversely 

 obloug in A. Opening of tube oblique or nearly vertical, 

 visible or hardly visible from above, complete or incomplete 

 distally (or basally). Oral shelf forming a trifoliate arch in 

 B, with a series of marginal sockets or alveoli, each of which 

 receives a tooth of the closed operculum ; in a forming a 

 rounded arch, b opercula with strong A-shaped main sclerite 

 and a series of extremely strong, curved submarginal teeth, 

 each of which fits into a distinct socket in the calcareous 

 part of the zocEcium when closed. A opercula transversely 

 oblong, with basal sclerite and without teeth. 



Channel between Mer and Dauer, Murray Islands, Torres 

 Straits, March 12th, 1889, Haddon Collection (C. M., 24.2.98). 



This species was obtained, well preserved, in spirit, and 

 by its means I have been able to make out some of the details 

 of the structure of the genus; these I hope to publish sub- 

 sequently. The species is in some ways the most interesting 

 of all, the evolution of the b opercula reaching their highest 

 point. They are moved b}' enormous muscles, and the occur- 

 rence of sockets to receive the points of the teeth is a unique 

 feature in the genus. The excessive rarity of the a zooecia 

 is another remarkable feature ; in one mounting I counted 

 only 6 A to 198 b; in another case 3 a to 86 b. 



The description is based on a single piece, of Hemescharan 

 habit. The zooecia are in the usual longitudinal rows, and are 

 very regularly quincuucial. The edge is slightly raised and 

 thin ; and the oral arch is hardly higher than the edge of the 



