3.36 AMERICAN JOURNAL 



They are of the most extreme tenuity. The apex of the septum 

 is a small, triangular knob, from which a large thin loop is di- 

 rected posteriorly. In the specimen this is not quite perfect, 

 but the loop when perfect is evidently entire. 



The interior of the neural valve is broadly sulcate on each 

 side of a faint mesial ridge, the sulcations corresponding to the 

 carinae. The muscular impressions are close in near the cavity 

 of the beak. There is a sharp ridge or septum just inside of the 

 foramen from one side of it to the other. 



The punctures are very large, circular, and under the glass re- 

 call the cells of Polyzoa. The margin of the valves is sharply 

 crenulated from the extremities of the external plications. 



The nearest ally of this species is Magasella Evansii, from 

 which it is readily distinguished by its form, color, foramen, 

 sharp plicae, form of the septum and other minor details. It 

 best agrees with the description of King's species. 



Length 1-04 in., breadth 1*03 in., diameter -52 in. 



Magasella (?var.) l^evis, Dall. PI. vi, fig. 9, 10, 13. 



f Terehratula Malvince, D'Orb., Voy. Am. Merid. v, p. 674, 

 No. 779, ix, pi. 85, f. 27, 29. 



Hob. Orange Harb., Patagonia. Smithsonian Cabinet, 

 11,782. 



Shell perfectly smooth except for the light, but beautifully 

 regular, rounded, concentric lines of growth. Outline nearly 

 circular, beak somewhat produced, slightly recurved, with a 

 large incomplete horse-shoe-shaped foramen. The false area 

 sharply carinate and separated from the deltidia by a deep 

 groove. The deltidia are short, moderately wide and widely 

 separated. Shell not inflated, of a horn color, and conspicuous- 

 ly punctate. Margin of the valves straight, without any inden- 

 tation or flexure. Teeth and sockets slender and weak, the 

 whole texture of the shell being exceedingly delicate and papy- 

 raceous. 



The cardinal process is hardly perceptible. The hinge plate is 

 very thin, excavated, and covers the posterior end of the mesial 

 ridge which divides the cavity of the beak below the hinge plate 

 into two parts. The crura are very short and delicate, the 

 haemal processes at first slender, rapidly widen, throwing off" a 

 triangular lamina of shelly matter from the inner sides which 

 reaches the septum and become consolidated with it between 

 the anterior and posterior edges, so that the posterior edge of 

 the septum forms a wall between the two triangular laminjB. In 

 the last species the edge does not project above the lozenge- 



