ART. 23 NEW PENTAMEROID BRACIIIOPODS FROM ALASKA KIRK 3 



The surface of the valves is marked by strong plications that 

 multiply by simple dichotomy. There are also fine wavy concentric 

 growth lines. The shell substance is fibrous, the fillers being intri- 

 cately twisted and contorted. 



The pedicle valve is smoothly convex or flattened and has a broad, 

 slightly elevated median fold. The beak is somewhat everted and 

 shows slight tendency toward incurving. The delthyrium is large 

 and when freed from the matrix the shallow spondylium is cleai-ly 

 seen. Bordering the delthyrium are narrow deltidial plates. 



The spondylium is attached to the inner borders of the delthyrium, 

 but so far as it has been possible to ascertain from sections it is not 

 supported by a septum at any point. In this feature the genus differs 

 from all other known pentameroids. It may be that in very early 

 growth stages the spondylium is adherent to the inner surface of 

 the pedicle valve or that a septum is present. If so, this condition 

 obtained only in the extreme posterior portion of the valve, and tlie 

 most careful sectioning has failed to show it. 



The brachial valve has a broad shallow median sinus correspond- 

 ing to the fold of the pedicle valve. Its apical portion is strongly 

 incurved. The septa of the brachial valve are low, short, widely 

 separated, and strongly divergent. They are inclined toward one 

 another and bear inclined crural processes. In the figure given the 

 processes have some adherent matter that somewhat obscures their 

 exact outline in part. 



There is no known pentameroid that closely approaches Gynibi- 

 diutn in structure. Superficially the form suggests a somewhat 

 aberrant C&rhchidium^ and as noted above it also suggests an orthoid 

 in its general habit. Internally the spondylium of the pedicle valve 

 most nearl}^ resembles that of Barrandella^ which is likewise free for 

 the greater part of its length, and also has an incipient septum that 

 does not reach the valve. The septa and crural processes of the 

 brachial valve are not essentially different from those of ConchidiuTH 

 except for their shortness and wide divergence. 



This genus so far is known only in the upper Silurian limestones 

 of Southeastern Alaska. 



Genotype. — Gynibidium acutum, new species. 



CYMBIDIUM ACUTUM. new species 



The only specimen preserving both valves has a small part of one 

 side broken off, so exact measurements of width can not be given. 

 This specimen has an approximate maximum width of 33 mm., a 

 maximum height of 28 mm., and a maximum depth of 20 mm. The 

 hinge line is approximately 22 mm. in length. The valves are almost 

 equally convex, although the brachial valve is somewhat more so. 



