4 PEOCEEDINGS OF THE NATTOISrAL MUSEUM vol. 69 



The pedicle valve with its projecting beak is, however, the larger. 

 The maximum breadth falls in the anterior half of the valves. 



The pedicle valve has a broad slightly elevated median fold that is 

 scarcely to be detected except in an anterior view of the shell. The 

 valve is deepest in its median anterior portion. From this median 

 line the shell carries around the beak, breaking abruptly toward the 

 delthyrium and forming a well defined but narrow, smooth cardinal 

 area. The beak is acute, everted, and shows but a slight tendency 

 towards incurving. The delthyrium is triangular in outline and is 

 proportionately large. It is bordered on both sides by narrow del- 

 tidial plates, which rest in shallow grooves. The spondylium is at- 

 tached to the inner margins of the delthyrium and then carries 

 forward and dorsad into the brachial valve, where its free margins 

 come in contact with the inner surfaces of the crural processes that 

 are supported by the septa of the brachial valve. So far as seen 

 the spondylium receives its sole support from the fusion of its pos- 

 terior margins with the inner border of the delthyrium. Sections 

 in the extreme apical portion of the valve show a secondary thicken- 

 ing of the valves and a filling of lime that would completely hide 

 a union of septum and valve, if such were ever present, which seems 

 doubtful anyway. The spondylium is known to be free and without 

 sign of a septum within two miLimeters of the tip of the valve. 



The brachial valve has a broad shallow sinus, corresponding to the 

 fold of the pedicle valve. The valve is deepest and most convex in 

 its posterior portion. The apical portion is strongly incurved. The 

 septa of the brachial valve are low and short, probably not having a 

 length exceeding 8 mm. in the type specimen. They diverge sharply 

 and widely from their points of inception. In section the septa are 

 shown to be inclined toward one another. Supported by the septa 

 are narrow inclined crural plates. 



The shell substance is fibrous, the fibers running and twisting in all 

 directions. The surface ornamentation consists of coarse plications 

 and fine concentric growth lines. The plications are most pro- 

 nounced in the median portion of the valves, becoming lower later- 

 ally and finally dying out near the delthyrium and hinge line. The 

 plications increase by regular dichotomy. 



This species is fairly abundant in the dark crystalline upper 

 Silurian limestones northeast of Edna Bay on the south shore of 

 Kosciusko Island, Southeastern Alaska. Collector, Edwin Kirk. 



Holotype and paratypes.—Cfii. No. 71036, U.S,N,M, 



CYMBIDIUM RETRORSUM, new species 



At a stratigraphically lower horizon and near the type locality of 

 Cymhidmm acutuni a second species of the genus was found. Two 



