66 DR. T. DAVIDSON ON RECENT BRACHIOPODA. 



resemblance to those of Zeilleria ; but the position of the larger-sized adductor muscles 

 is no longer the same as in Waldhelmia, while the complete absence of a mesial septum 

 and the shape of the largely divided hinge-plate wovild, in his opinion (Deslongchamps'), 

 be valid grounds for separating the genus Macandrevia from Waldhelmia. 



35. Waldheimia (Macandrevia) tenera, Jeffreys, sp. (Plate XII. figs. 6-10.) 



Terebratula tenera, Jeffreys, Ann. & Mag. Nat. Hist. 4th ser. vol. xviii. p. 250, 1876, and Proc. 

 Zool. Soc. 1878, p. 405, pi. xxii. fig. 7. 



Shell rather small, extremely thin and delicate, oval, longer than wide, rounded 

 laterally, less so in front ; surface smooth, marked only by fine concentric lines of 

 growth, and perforated by minute canals. In the interior of the dorsal valve po cardinal 

 process is observable ; hinge-plate comparatively large, and divided into two parts by a 

 narrow mesial depression, between which, in the middle, a very narrow delicate longi- 

 tudinal ridge or rudimentary septum is present, which extends to about one fifth of 

 the length of the valve. The inner slopes of the hinge-plate extend likewise in the 

 shape of two septa of small elevation to about the same distance, first diverging, then 

 converging to the anterior extremity of the small median ridge. At the base of the 

 hinge-plate the principal delicate stems of the loop are attached, and these extend to 

 about two thirds of the length of the valve before they are reflected. Colour light 

 brown. Length 6, breadth 4, depth 3 lines. 



Hab. Dredged by Dr. Gwyn Jeffreys during the return voyage of H.M.S. ' Valorous ' 

 from Davis Strait, in lat. 56" 11' N., long. 37° 41' W., at a depth of 1450 fathoms, 

 on a sea-bottom of Globlf/erlna-ooze and stones. 



Obs. I have seen two or three perfect examples of this extremely delicate species, 

 brought home by Dr. Gwyn Jeffreys. The shell seemed full-grown. A specimen about 

 one line in length showed traces of one of its early stages of growth, in the presence of a 

 small vertical septum, at about half the length of the valve, to which the loop at that age 

 had an attachment, as Friele has so well described to be the case in Waldheimia cranium. 



Dr. Gwyn Jeffreys observes that " this species differs from T. cranium in being only half 

 the size in exact measurement, and consequently one fourth in bvilk ; it is of a different 

 shape, texture, and colour, compressed instead of convex, having a much shorter beak 

 and smaller orifice, with not half the proportionate number of tubei'cles ; and the blades 

 are closer together, and do not extend so far towards the front. In the young of each 

 species the comparative number of tubercles and prominence of the beak are distinctly 

 marked ; and the septum in the present species is shorter, although conspicuous and 

 gnomon-shaped." 



Uncertain Species. 



36. Waldheimia Wyvillii, Davidson. (Plate X. figs. 5, 6.) 



Waldheimia Wyvilli, Davidson, Proc. Roy. Soc. vol. xxvii. p. 438, 1878; and {W. tvyvillii) Report 

 on the Bracliiopoda, Voyage of H.M.S. ' Challenger,' Zool. vol. i. p. 44, pi. iii. figs. 13 a, b, 1880. 



Shell ovate or longitudinally oval, very thin, semitransparent, light brownish yellow, 

 smooth, marked at intervals by concentric lines of growth. Dorsal valve moderately 



