137 



have been made from imperfect specimens. I have searched in vain 

 for the Siliquaroid windlass and fringe and the Polystomelloid loculi. 



The ordinary shape is like that of a common brown ha-in — Hat in 



the middle, where t ho spiral elements are rerj rarely discernible, 

 with the sides flattened, diverging at a greater or less angle, and 

 with a Btrong rib bounding the medial portion, and proceeding 



in about seven spiral turns (or less) t,, the periphery. Although 

 presenting analogies with the opercula of Borne of the Bivonue, it 

 appears much more nearly related to the Turritellida, from which 

 it differs in being bent outwards instead of inwards. The peculiar 



characters are not so constant as might he expected, and perhaps 

 depend in part on the amount of contraction of the animal in drying. 

 One specimen was found with hut very slight excurvation : a few 



were pretty regularly convex, instead of being trigonal ; and in these 

 the central area was not marked off by the rib, which proceeded I I 

 lose itself gradually towards the apex. The flattened part is about 

 the size of the first tube of the shell ; the whole diameter, about 

 012. The spiral rib is also found, more or less developed, in 

 species with a concave operculum. 



The Drochus arcuatueoi Brown proves to be a veritable Brochina 

 glabra in a transition state. After I had described and returned 

 Mr. Alder's apparently plugless specimen, it came in two in his 

 hands, displaying a duly formed plug in the middle. The decollated 

 portion, which was abnormally persistent, having been open, seems 

 to favour the hypothesis I had ventured to suggest from the com- 

 plex character of the plugs in Caecidse, that they are not mere septa 

 continually cast off and renewed, but an integral part of the struc- 

 ture, removed from time to time with additional layers. Some emi- 

 nent naturalists, however, state that this is impossible. 



37 b. ? Brochina ? glabra. 



Hub. W. Indies, in sponge of commerce. 



Very few W. Indian specimens were found of this form ; and of 

 these only three were sufficiently perfect to allow of identification. 

 These did not present any characters, by which they could be distin- 

 guished from the European species ; hut they await a knowledg 

 the operculum. 



38. ? Brochina glabrifokmis, Cpr. 



I B. t. " B. glabrae" nmillima, eed ■•<>■}>?<> mamillato tnmeni 

 fere hemisphcerico : operculo .'.... 



Long. -07.'i, lat. ■()]?. 



Hub. Mazatlan, extremely rare. Has. Brit. *\'- 



Maz. Cat. p. 327. 



This species is kept provisionally separate, at leasl ,; ll the opercu- 

 lum has been examined. The -lull alone affords no satisfaci 

 mark of specific separation. 



