DE. T. DAVIDSON OX RECENT BEACHIOPODA. 95 



Magasella crenulata, Dall, A Revision of the TcrcbratulicUe, Amer. Journ. of Conch, vol. vi. p. 137, 

 1870; and Proc. Acad. Nat. Sci. Philadelphia, 1873, p. 188. 



Shell suborbicular, about as wide as long, margin rounded laterally, subtruncate in front. 

 Dorsal valve moderately and uniformly convex, without fold or sinus. Ventral valve 

 rather deeper than the dorsal one ; beak produced, slightly incurved and truncated by a 

 large complete foramen, separated anteriorly from the hiuge-linc by a deltidium in two 

 pieces ; beak-ridges sharply defined, leaving between them and the hinge-line a flattened 

 false area. Marginal line flexuous and slightly sinuated in front. Surface of the valves 

 often smooth at the beak and umbo, or marked throughout with from twenty to twenty- 

 two rounded ribs, of which a few are due to the interpolation of shorter ones. In the 

 interior of the dorsal valve the loop is doubly attached, first to the hinge-plate, secondly 

 to an elevated mesial septum. Colour light yellowish white. Length 8, breadth 8, depth 

 4 lines. 



Hab. Santa Cruz, Canaries (Cuming). 



Obs. This small species still requires further study before being definitely admitted. 

 The material I have had for examination consisted of only three examples. It is much 

 more circular than Gould's Magasella patagoiiica, and seems to difi^er likewise from 

 specimens of Terebratella Oorsata of similar dimensions. The foramen was entire in 

 the few examples that have come under my observation. 



51. Magasella aleutica, Dall. (Plate XVII. figs. 16-17 h) 



Magasella aleutica, Dall, Preliminary Descriptions of new Species of Mollusca from the North-west 

 Coast of America, Proc. California Academy of Sciences, vol. iv. pi. i. fig. 6, 1872; and Proc. Acad. Nat. 

 Sci. PhUadelphia, 1873, p. 188. 



Shell small, ovate, greatest breadth about the middle, tapering posteriorly and 

 anteriorly, slightly indented in front. Dorsal valve convex, most so near the umbo, with 

 a very slight longitudinal depression commencing at about the middle of the valve and 

 extending to the front. Ventral valve not much deeper or more convex than the dorsal 

 one, margins nearly straight ; beak short, incurved and truncated by an incomplete 

 foramen, margined anteriorly by the umbo and by two small lateral deltidial plates ; beak- 

 ridges not sharply defined. Surface smooth, marked only by concentric lines of growth; 

 salmon-coloured, brighter on the lines of growth, pale on the umbones. Length 6 lines, 

 breadth 7, depth 3^ lines. Loop doubly attached, very slender, except the lateral arms 

 of the reflected portion, which are wide ; septum rather broad from behind forward, not 

 produced above the reflected portion of the loop. 



Hub. In the Aleutian Islands, from Akeutan Pass to the Shumagins, attached to the 

 under surface of rocks at extreme low water in spring-tides (Dall). 



Obs. I have two examples of this small species presented to me by Mr. Dall, and in 

 sending them to me he wrote : — " In regard to Magasella aleutica I am disposed to 

 consider it an adult species, for very thorough dredgings in the region where it is common 

 have failed to indicate any other species of which it might be the young. I have seen 

 young Terebratella frontalis, and they appear to differ specifically from Magasella 



