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Show 1886.] OF THE GENUS ATRETIA. 183 and compressed, bears no resemblance whatever, and exhibits at all ages definite generic characters1. ATRETIA BRAZIERI, sp. nov. Description.-This pretty little Brachiopod presents all the well-marked characteristics of the 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 the 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 surrounded by muscular scars (?) in the exteriors of the ventral valves of two specimens I have examined under magnifving-powers. The shell is shallow towards tbe 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 2^ lines ; width IJ 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 ad 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 m y old and valued friend to describe the species 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 conchologists thereto, and to place on record the wide geographical distribution of tbe genus Atretia, which we now know to range in from 25-1750 fathoms, from nearly 70° N. 1 NOTE.-I communicated the discovery of the Australian Atretia to the Norwegian naturalist, Herr Herman Friele, who replied, April 19tli, that my description of the skeleton of A. brazieri is quite typical of the genus Atretia, which he cannot consider to be the young of Rhynchonella. H e adds the important fact that he obtained some fifty specimens of the Atretia gnomon, Jeff'r., during the Norwegian North-Atlantic Expedition, but no Rhynchonella occurred on the same station or in corresponding depths.-AGNES CRANE, April 26th. |
