PLATE IV G. 



Legend. B. Bracliial valve. 

 P. Peilicie-viilve. 

 F. Foramen. 



J). Pedicle-callosity (in brachial valve). 

 g. Pedicle-groove, 

 g'. Ba.se of groove. 

 1. Walks of groove, 

 s. Median septnm. 

 o. Posteiior niusculai' scai'S. 



Fig. 



Fig. 



Fig. 

 Fig. 



Fig. 

 Fig. 



Fig. 



Fig. 



Fig. 

 Fig. 

 Fig. 



Fig. 



Fig. 

 Fig. 



Fig. 



Fig. 

 Fig. 



c. Central .scar.s. 

 pc. Posterior centrals, 

 cc. Median centrajs. 

 ac. Anterior centrals. 

 )ia. Posterior addnctors. 

 pa'. Antei-ior element of 

 ductoi's. 

 aa. Anterior addnctoi-s. 



posterior ad- 



TREMATIS, SiiARi'K. 



i'age 13S. 



Tkematis tekminalis, Emmons. 



Fig. 1. The infei-ior of a bi-achial valve; showing the posterior and central muscular .scars and the lingui- 



forni median elevation. X 'i- 

 Fig. 2. An internal cast of the pedicle-valve ; showing the great depression of the pedicle-area, the 



me<lian ridge ccn-respomling to the pedicle-groove, and the vascular sinuses. X 3. 

 Trenton limestone. MlddlevUle. N. Y. 



Trematis, .sp., tompaio T. punctosxhiata, Hall. 



3. The internal pe<licle-area ; showing the elevation of the margins of the tissui-t 

 Hudson River gronji. Frankfort, Ky. 



X 4. 



TUEMATIS MILLIPUNCTATA, Hall. 



4. The intei'i(^r of a brachial vah"e ; showing the postei-ior callosity foi'niing a surface for the passage 



of the pedicle, the external muscular scars and the components of the central impressions. X 2. 

 Hudson River group. Covington, Ky. 



5. An internal cast of a brachial valve, to which a portion of the shell adheres. X 2. 



6. The exterior of a brachial valve, from which the shell is partially exfoliated. X 2. 



7. Protile of an internal cast of the conjoined valves. 



8. Anterior view of the same specimen, exposing the pedicle-valve and the projecting apical portion 



of the brachial valve. X 2. 



Cincinnati, Ohio. 

 showing the posterior muscular scars beneath the liroken pedi- 



9, 



10. 



Hudson River group. 

 The interior of a brachial valve : 

 cle-callosity. X 1 i>. 



Hudson River group. 

 The external ornamentation. X 



Frankfort, Ky. 



Hall. 



Trematis ruNcrosTRtATA, 



11. The exterioi' of a brachial valve. X 2. 



12. The interior of a pedicle-valve. X 2. 



13. The external ornamentation. X 25. 



Trenton limestone. Clifton, Tenn. 



Trematls fragilis, Ulrich. 



14. A pedicle-valve ; showing the short and narrow pedicle-tissure. 



Hudscm Rivei- group. Bank Lick Creek, Ky. 



Trematis Ottawensis, Billiiig.s. 



1.5. External view of a brachial valve. From a gutta-percha cast of the exterior. Natural size. 



16. The surface ornamentation. X 2.5. 



Trenton horizon. Frankfort, Ky. 



17. The external pedicle-area, from a specimen i-eferred with doubt to this species. X 3. 



Hudson River grouji. Cincinnati, Ohio. 



Trematis umbonata, Uhith. 



18. The exterior of the brachial valve. X 2. 



19. The same specimen, with the upper portion of the bi-achial valve removed, exposing the Hat lower 



valve and its pedicle-tissure. X 2. 

 From the original specimen figured l)y Ulhich (Amei-ican Geologist, vol iii. No. tj, p. 378, tig. 8. 

 1889). Hudson River group. Covinytim, Ky. 



