NO. 7 SILICIFIED ORDOVICIAN BRACHIOPODS — ROSS AND DUTRO 21 



EXPLANATION OF PLATES 



Plate 1 



(All specimens from USGS coll. D1072 CO) 



Figs. 1, 3, 5. Rhynchotrema? sp. Brachial, pedicle, and right lateral views, X 2, 

 the only specimen obtained, USNM 145323. 



Figs. 2, 4, 6, 8. Ptychopleurella cf. P. lapzvorthi (Davidson) X 5. 2, 4. Pedicle 

 and brachial views of a complete specimen, USNM 145324; 6, pedicle in- 

 terior, USNM 145325; 8, brachial interior, USNM 145326. 



Figs. 7, 9, 10, 15, 17-20. Catazyga homeospiroides Ross and Dutro, n. sp. 7, 9, 

 10. Brachial, pedicle, and left lateral views, X 2, holotype, USNM 145327; 

 15, brachial view, X 4, immature specimen, USNM 145328; 17, brachial 

 interior view, X 2, showing base of loop, divided hinge plate, and absence 

 of cardinal process, USNM 145329; 18, view through break in pedicle 

 valve, X 2, showing part of loop, USNM 145330; 19, 20, exterior and 

 interior views, X 2, of a pedicle valve, USNM 145331. 



Figs. 11-14, 16. Camerella? sp. X 2. 11, 12, 16. Pedicle, brachial, and right 

 lateral views of a complete specimen, USNM 145332; 13, 14, interior and 

 exterior views of pedicle valve, the only specimen which shows the spon- 

 dylium, USNM 145333. 



Plate 2 

 (All specimens from USGS colln. D1072 CO) 



Figs. 1, 3, 5, 7, 9. Anoptambonites cf. A. grayae (Davidson), X 2. 1, 3. Interior 

 and exterior views of a damaged brachial vavle, USNM 145334 ; 5, interior 

 showing only the visceral disc ("lophophore platform" of Williams, 1962) 

 of a broken immature brachial valve, USNM 145335; 7, 9, interior and 

 exterior of a pedicle valve, USNM 145336. 



Figs. 2, 4, 6. Cyclospira cf. C. glansfagea Cooper and Kindle, X 5. 2. Left 

 lateral view of a broken specimen showing part of the spire inside, USNM 

 145337; 4, 6, brachial and pedicle views of a complete specimen, USNM 

 145338. 



Figs. 8, 11, 13. Cyclospira? sp. Brachial, pedicle, and left lateral views, X 5, 

 USNM 145339. 



Figs. 10, 12. Diambonia cf. D. anatoli Spjeldnaes. Exterior and interior views 

 of a small pedicle valve, X 4, showing well developed septum and orna- 

 mentation of 5 ribs, USNM 145340. 



Figs. 15, 16. Diambonia sp. 1. Exterior and interior views of a pedicle valve, 

 X 2, showing relatively short median septum and only 3 ribs, USNM 

 145341. 



Figs. 18, 20. Diambonia sp. 2. Brachial and pedicle views of a complete speci- 

 men, X4, lacking any ribs, USNM 145342. 



Figs. 14, 17, 19. Whitfieldelfol. sp. Pedicle, brachial, and left lateral views, X 4, 

 USNM 145343. 



