284 RESEARCH IN CHINA. 



curve. Pedicle valve strongly elevated at the beak, the surface sloping from the 

 umbo to the anterior and antero-lateral margins with a slightly convex curve, some- 

 times becoming a little concave as it approaches the anterior margin, the slope to the 

 cardinal extremities somewhat more abrupt; cardinal area large, flat, sloping pos- 

 teriorly from the hinge-line in one specimen at an angle of 102 and in another at an 

 angle of 1 15 to the plane of the valve, the cardinal margins sharp ; delthyrium rather 

 narrow, closed with a strongly convex deltidium, foramen terminal, encroaching 

 upon the umbo; median septum inconspicuous; muscular impressions indefinite, 

 rather large, and flabelliform. Surface of each valve marked by fine radiating costae, 

 two or three of which occupy the space of i mm. 



The dimensions of two pedicle valves are: length 15 mm. and 14 mm., width 

 18.7 mm. and 16.9 mm., height of cardinal area 5 mm. and 5 mm., greatest width of 

 deltidium 3 mm. and 2.5 mm. The dimensions of a brachial valve are: length 16.5 

 mm., width 21 mm., convexity 4 mm. 



This species i; represented in the collection by only a small number of speci- 

 mens, none of which are as well preserved as might be desired. It differ.; especially 

 from other members of the genus in the terminal position of the pedicle opening, the 

 pedicle apparently having passed through the foramen in a direction continuous 

 with the surface of the deltidium and not at an angle to it, as is usually the case. 

 This position of the pedicle also seems to have modified the position of the spon- 

 dylium, its surface being nearly vertical to the inner surface of the valve, in con- 

 sequence of which the median septum becomes essentially obsolete. 



Hemipronites tenuistriata Weller (plate 25, figs 21-24). 



1907. Hemipronites tenuistriala Weller, Proc. U. S. Nat. Mus., vol. xxxn, p. 559. 



Shell wider than long, the valves subequally convex, the hinge-line a little 

 shorter than the greatest width, the cardinal extremities subangular. Pedicle valve 

 most prominent on the umbo, the beak rather obtuse, the surface sloping from the 

 umbo laterally and anteriorly with a gently convex curve ; a slight, scarcely noticeable 

 mesial flattening of the valve occurs toward the front, but no mesial sinus is present; 

 cardinal area flat, rather large, with a broad deltidium, the cardinal margins angular. 

 Brachial valve most prominent along the median line, but with no differentiated 

 median fold, the greatest convexity at about the mid-length of the valve, the surface 

 slightly compressed toward the cardinal extremities. Surface of each valve marked 

 by exceedingly fine striae which are scarcely visible to the naked eye, about eight 

 occupying the space of i mm. 



The dimensions of a pedicle valve are : length 16 mm., width approximately 17.5 

 mm., convexity 5 mm., height of cardinal area 3 mm., length of hinge-line 15 mm. 

 The dimensions of a brachial valve are: length 17 mm., width 22 mm., convexity 5 mm. 



The specimens of this species in the collection are all too poorly preserved to 

 allow the determination of its generic position with entire satisfaction. They have, 

 however, the general form of European members of the genus Hemipronites and it 

 is believed that this generic reference is correct, but the nature of the deltidium and 

 the presence or absence of a foramen can not be certainly determined. The genus 

 Hemipronites has not been recognized in the American faunas, and is known espe- 

 cially from the Baltic provinces in Russia. The species is evidently congeneric 

 with th'j shell which Marielli has called Orthisina giraldii? and the two species are 

 closely allied. The species here described, however, is somewhat more finely striate, 

 and it seems to be relatively a somewhat broader shell. 



'Boll, delta Soc. Geol. Ital., vol. xx (1901), p. 305. 



