PLATE Va. 



(Figures 2, 4, IG-il, 24-10 h\ V,. F.mmcins; I, :;, j-ll by 1!. P. Wiutfiklk ; !■"> bv K. I!. Mi-.kk ; '.'i bv riiii.ir A.M , 



■!■> by S. C. McCojf NKLL. ) 



Legend. A- Deltidiuni. a'. Posterior adductor impressions, 



j. Cardiniil process. r. Diductor muscular impressions, 



fji. Crural plate. p. Pedicle-musqular impression. 



t. Teeth. o. Ovai-ian impressions, 



li. Socliets. V. Vascular marking-s. 



a. Anterior adductor impressions. 



HEBKKTELLA, nom. nov. 



Page 19S. 



■Oethis sinuata, Hall. 



Fig. 1. The interior of a pedicle-valve ; giving' the chai'acter of the muscular area, ovarian and vasculai- 



markings. 

 Fig. 2. An enlargement of the muscular area of the pedicle-valve ; showing the large diductor (r), lineal 



central adiluctor («) and the pedicle-scar (p). X 2. 

 Fig. 3. The interior of a brachial valve. 

 Fig. 4. The muscular and deltirlial area of the brachial valve ; showing the narrow, slightly thickened 



cardinal process (./), the large crural plates and the quadi'ipartite impression of the adductor 



nniscles. X 2. 

 Fig. 5. The exterior of a brachial valve. 

 Figs. 6, 7. Cai-dinal and protile views of the same specimen. 



Fig. 8. ExteHor of the pedicle-valve ; the area and delthyrium of the opposite valve showing. 

 Hudson River gi-oup. Cincinnati, Ohio. 

 For further illustration see Palaeontology of Ohio, Volume I, plate ix, fig. 4. 



Orthis sinuata, Hall. (?) (Compare 0. Maria, Billings.) 



Fig. 9. A view of the brachial valve and protile of a specimen doubtfully referred to this species. 



Hudson River group. , Ohio- 

 Fig. 10 = 19, by eri'oi-. 



OliTHIS OCCIDENTALIS, Hall. (?) 



Figs. 11, 12. Views of a small specimen wth coarse, simple plications, and the median sinus incipiently 

 developed ; probably the young of this species. 



Hudson River group. Savannah, Illinois. 



-. -ii .Si;.-// Orthis insculpta, Hall. 



Fig. 13. The interior of a pedicle-valve ; showing the muscular, vascular and ovarian markmgs. X 2. 

 Huiison River group. Oxford, Ohio. 

 For further illustration see Palaeontology of Ohio, Volume I, plate ix, tig. 1. 



PL.E.SIOMYS, NOM. NOV. 



Page IM. 



Orthis retrorsa, Salter (= O. Carki/t, Hall). 



Fig. 14. The interior of a pecicle-valve ; showing the short dental lamellie, suljquadrate muscular area, 



the vascular and ovarian makings. 

 Fig. 15. A view of the pedicle-valve of the orignal specimen ; showing the high area and retroi'se beak of 



this valve. 

 Fig. 16. Profile of a large individual ; showing the great convexity of the brachial valve and the degree of 

 resupination of the beak of the pedicle-valve. 

 Hudson Ri\er group. Oxford, Ohio. 

 For further illustration, see Palseontology of Ohio, Volume I, plate xi, fig. 7. 



Orthis subquadrata, Hall. 



Fig. 17. The interior of the pedicle-valve ; showing the component scars of the subquadrate muscular area, 



the lateral ovarian ai-eas and the vascular impressions ovei- the pallial region. 

 Figs. 18, 19. Brachial and cardinal views of a normal individual. 

 Hudson River group. Oxfm-d, Ohio. 

 For further illustration, see Palfeontology of Ohio, Volume I. plate ix, fig. 2. 



