NO. 7 SILICIFIED ORDOVICIAN BRACHIOPODS ROSS AND DUTRO I J 



Genus PTYCHOGLYPTUS Willard, 1928 



PtycHoglypbus? cf . P? pauciradiatus Reed 



Plate 3, figures 18, 19 



Ptychoglyptus paiiciradiatus Reed. Reed, F. R. C, 1932, Skrift Norske Vidensk- 

 Akad. Oslo I. Mat-Nat. Klasse, No. 4, pp. 122-123, pi. 18, figs. 1, 2. 



Description. — Shell thin, concavo-convex, roughly semicircular, 

 wider than long with greatest width at hinge line ; surface with seven 

 primary costellae between which are many finer capillae; regular 

 concentric wrinkles interrupt the capillae but do not cross the pri- 

 mary costellae; wrinkles are uniform except in the sectors on the 

 ears. No internal structures available for study. 



Discussion. — A single well-preserved complete specimen is tenta- 

 tively referred to this species. The Alaskan specimen possesses 7 

 principal costellae, rather than the 5 of P. bellarugosus Cooper from 

 the Gaspe. At a distance of 5 mm from the umbo there are about 

 20 secondary capillae between the larger costellae. Concentric wrinkles 

 are closely spaced, simple, and aligned transversely from one sector to 

 the next, a characteristic which distinguishes the specimen from many 

 species of the genus as well as from P. bellarugosus. 



Although one can hardly discuss a species on the basis of a single 

 specimen, it can be noted that this shell resembles P. virginiensis in 

 number of primary costellae but that concentric wrinkles are far more 

 regularly and closely spaced. P. ambiguus Reed possesses twice as 

 many large radial costellae. In P. ulrichi Endo many of the radial 

 costellae are intercalated and closely spaced and concentric wrinkles 

 are very irregular. Costellae are also more closely spaced in P. 

 shanensis Reed, in which transverse wrinkles are chevron-shaped 

 within each sector. Larger costellae of P. valdari Spjeldnaes are far 

 more numerous than in the Alaskan specimen and the concentric 

 wrinkles are irregularly spaced from one sector to the next. 



The specimen from Alaska is very similar to P. pauciradiatus Reed 

 both in radial and concentric ornamentation. Reed's species is from 

 the Upper Ordovician Hovin Sandstone of the Trondheim area, 

 Norway. On the other hand, the Alaskan specimen is also similar in 

 ornamentation to an immature (?) shell of comparable size from low 

 in the Caradoc, referred by Williams (1962, p. 160, pi. 14, fig. 34) to 

 Glyptambonites aff. G. glyptus Cooper. 



Figured specimen. — USNM 145354. 



