1886.] OF THE GENUS ATRETIA. l'*-'^ 



and compressed, bears no resemblance whatever, and exhibits at all 

 ages definite generic characters \ 



Atretia brazieri, sp. nov. 



Description. — This pretty little Brachiopod presents all the well- 

 marked characteristics of tlie genus, two short curved slender 

 processes, denticulated at their extremities, descend from the small 

 narrow hinge-plate of the smaller dorsal valve, and an elevated wedge- 

 shaped projection rises abruptly from tlie central mesial septum of 

 the same valve. The presence of this septum is indicated by a dark 

 line visible from the exterior of the shell. The shell is small, 

 generally longer than wide, triangular in shape, especially in the 

 younger specimens. Dorsal valve rounder and not so large as the 

 ventral one, slightly flexuous towards the centre at the margins of 

 the valves. The ventral valve, owing to the prolongation of the 

 beak area, is longer and more triangular than the dorsal one raised 

 towards the beak, which is slightly produced and incurved, with a 

 triangular foramen commencing beneath its pointed extremity. Two 

 elevated ridges extend from the shoulder of the shell nearly to the 

 margins of the valves, and there seems to be a slight elevation 

 corresponding with the well-marked exterior depression and sur- 

 rounded by muscular scars (?) in the exteriors of the ventral valves 

 of two specimens I have examined under magnifying-powers. The 

 shell is shallow towards the margins, but rounded and deeper near 

 the beak. Shell-substance imperforate ; surface smooth, glossy, and 

 gleaming, marked with fine concentric lines of growth; semitrans- 

 parent, Horn-coloured or light grey. 



Length 2j lines ; width 1^ line; depth about 1 line. Another 

 specimen measured 2 lines in length by 2\ in width ; this was more 

 flattened and depressed, and the external mesial sinus in the ventral 

 valve was less marked. Other specimens were about 1 line in length. 



Station and Depth. — Eleven specimens and odd valves were 

 dredged in twenty-five fathoms in sandy mud off Cabbage-Tree 

 Island, Port Stephens, N.S.W., by Mr. John Brazier, who sent five 

 specimens to Dr. Davidson, with the remark that they differed from 

 all other known Brachiopoda from Australian waters. 



Obs. — Dr. Davidson commemorated Mr. Brazier's discovery by 

 naming the species after him, and I have deemed it my duty to my old 

 and valued friend to describe the specie? under the name he desired 

 to give it, as well as I am able. In so doing I wish to call the 

 attention of qualified conchologisls thereto, and to place on record 

 the wide geographical distribution of tiie genus Atretia, which we 

 now know to range in from 2,5-1750 fathoms, from nearly 70"' N. 



^ Note. — I coniniunicated the discovery of the Australian Afrcfia to the Nor- 

 wegian naturahst, Herr Herman Friele, who replied, April 10th, that my 

 description of the skeleton of A. hra~icri is quite typical of the genus Atrcfia, 

 which he cannot consider to be the young of RhynawncUa. He adds the im- 

 portant fact that he obtained some tift y specimens of the Atretiu gnomon. Jcfi'r., 

 during the Norwegian North-Atlantic Expedition, but no lihynchoneUa occuri-ed 

 on the same station or in corresponding depths. — Aonks Crank, April 26th. 



