DR. T. DAVIDSON ON RECENT BRACHIOPODA. 143 



Shell small, transversely oval, wider than long- ; hinge-line straight, rather less than the 

 breadth of the shell, sides and front rounded. Dorsal valve semicircular, very little 

 convex, somewhat flattened. Ventral valve deeper than the dorsal one, Avith a slightly 

 marked depression extending from the beak to the anterior margin ; beak bent backwards 

 and truncated by a large incomplete foramen, xxsually much eroded, margined ante- 

 riorly by the umbo and laterally by very small rudimentary dcltidial plates ; area 

 triangular, flat, and smooth. Colour light brownish white, with about twelve radiating 

 ribs in each valve, of which five or six are smaller and interpolated between the longer 

 ones. In the interior of the dorsal valve a large, much elevated mesial septum is 

 present, denticulated anteriorly, forming nodules and iiotches on its upper edge, the 

 whole having a subtriangular form, somcAvhat resembling an open fan. The loop consists 

 of tAvo bands, or lamella?, attached to the hinge-margin and afterAvards to the sejitura on 

 each side about its middle and close to the shell. Cardinal plate, or hinge-plate, absent ; 

 area behind the muscular disk somcAvhat excavated. Length 3 lines by 3J in breadth. 



Hah. Tortugas, in a depth of 30 to 43 fathoms (Pourtales). Ofl^ Havana, 80 to 127 

 fathoms (Sigsbee) ; Barbados, 100 fathoms, ' Blake ' Exped. (Dall). 



Obs. We are indebted to Mr. TTilliam H. Dall for the first description of the animal of 

 Cistella (C. litlea), Avhich he published in 1871, prior to Ivowalevsky's admirable 

 description of the animal of Cistella NeapoUtana in 1873, and that of C. KoicalevsJdi by 

 Schulgin in 18S4. Dall says (/. e. p. 20) : — " Muscular impressions much thickened, 

 forming two rather concave disks. . . . The anterior portion of the apophyses is 

 more posterior than in C. NeapoUtana, and the margin is not granulated as in that 

 species. It Avould seem from Mr. Davidson's figures that the loop of Cistella Barrettiana, 

 Dav., is more anterior than in this species ; the latter being also unprovided with the 

 posterior extension of the septum seen in the figure of the former, and being, moreoA'er, 

 entirely destitute of the red markings between the ribs ..... It is possible that the 

 present species, C. Anfillartim and C. Barrettkma, are forms of one species, in which case 

 the last name has priority." 



[_L. c. p. 22.] " I have not met Avith much success among these small species in the use 

 of acid in dissolving away the shell from the animal. . . . The brachia in this and the other 

 species oi" the genus are arranged around the edge of a broad membrane, Avhich covers the 

 concavity of the shell, like a drumhead. The loop of the drum is represented by the apo- 

 physes. The brachia diS"er from the same organs in the Terebnitulina; in being arranged 

 in a single series instead of a double one. Of this there can be no doulit, it is very evident 

 upon a casual inspection, and is entirely confirmed by careful dissections. In this species 

 the drumhead membrane is divided into two lobes by the septum. The edges of these lobes 

 are fringed Avith the brachia. . . . They are usually curled up in front and on each side, 

 Avhile those Avhich are situated behind the mouth are longer than the others, and usually 

 lie smoothly over them, extending forward without any marked curve, pointing toAvards 

 the anterior margin of the shell, and extending clear over the central membrane, even 

 beyond the posterior edge of the septum. The brachia are covered Avith an epithelium 

 furnished Avith cilia, are tubular, and communicate Avith a series of brachial channels, 



