DALL— BEACHIOPODA. d41 



flexuosity is visible only at the margin. Beak very low and small, the foramen minute, 

 entire ; the united deltidial plates at the foramen project like the lip of a pitcher ; there 

 is no marked area, a slight flattening on each side of the deltidium, with no emphasized 

 limits, may be observed under a lens. The margin of tlie pedicel valve is convexly 

 arcuate in the lateral cardinal region, then slightly depressed, to rise prominently in the 

 anterior medial region, where in most adult (but not senile) specimens the margin is so 

 undulated as to form two or three tooth-like projections fitting into corresponding notches 

 in the opposite valve ; in senile specimens these notches become irregular or obsolete. 

 The soft parts are normal, differing in general from those of M. psittaceu only in being 

 more delicate and translucent ; the ovarian sinuses in the pedicel valve extend forward 

 nearly to the anterior margin in two nearly straight, slightly converging main trunks, 

 each of which, about midway in its course, gives out on the external side a narrow lateral 

 branch, which also proceeds toward the anterior margin, near which it is slightly 

 branched like the main sinus. The hinge is that of typical Hemithyris, there is no trace 

 of a spondylium. The general character of the cardinal apparatus and of the rather 

 deep muscular impressions is best illustrated by the figures. Lon. 17'5, max. lat. 16"5, 

 diam. ll'O mm. 



This species differs from the shallow-water species, both north and south, in its colour 

 and delicacy, and also in having the foramen completed by deltidial plates. 



The only species with which it needs close comparison is Hemithyris lucicla, Gould, 

 of Japan. In this the beak resembles that of H. psittacea, in that its distal portion is 

 produced into a point so as to overshadow the foramen, and while the deltidia exist and 

 complete the foramen, instead of being convex and produced at the foramen into a sort 

 of spout, as in H. sladeni, they are impressed and almost concave ; the anterior flexuosity 

 of II. lucida also differs in being wide and sqiiared at the sides, with an invariably entire 

 and straight margin between the angles. S. lucida is also faintly microscopically 

 radiately striated, while H. sladeni is smooth except for incremental lines. 



The species is named in honour of the late Walter Percy Sladen. 



EXPLANATION OP PLATE 26. 



Fig. 1 . Liothyrina sp. : apophyses, x 7. 



Fig. 2. Spicules of Liothyrina sp. x 20. 



Fig. 3. Kranssina gardineri : interior of liEemal valve. 



Pig. 4. „ „ exterior of pedicel valve. 



Jig. 5. „ „ interior of pedicel valve. 



Fig. 6. „ „ anterior margin and profile. 



Fig. 7. Hemithyris sladeni : interior of pedicel valve. 



T?itr 8 ,, ,, interior of hsemal valve. 



Fig. 9. J, „ exterior of pedicel valve. 



Fig. 10. „ „ exterior of hsemal valve. 



Fig. 11. „ „ lateral profile. 



Fig. 12. „ » anterior profile. 



