PLATE 17 



Figs. Onniella broggeri Bancroft 



I, 6. — Dorsal and ventral views, showing exterior. 



Ordovician, Horderley District, E. Shropshire, Eng- 

 land. Cat. No. S 21 12. x2. 



Onniella sp. 



8, 12. — Dorsal internal mold and impression taken from it. 



9, 1 1 . — Ventral internal mold and replica of it. 



18. — Enlargement, x 4, of fig. 12, showing internal struc- 

 ture in greater detail. Cf. fig. 23. 

 Up. Ordovician, Horderley District, E. Shropshire, 

 England. Cat. No. S 2 1 1 3. All except fig. 1 8 x 2. 



Dalmanella rogata (Sardeson) 

 2,31. — Dorsal interior, x 2.65, and enlargement of same, 

 X 4, showing simple, bladelike brachiophores and car- 

 dinal process. The myophore is lobed and from its 

 center there has grown forward along the shaft a 

 peculiar process giving the whole the appearance of 

 the head of a bee. 

 Ordovician (Black River), St. Paul, Minn. Cat. 

 No. S 845. 

 3, 5. — ^Ventral and dorsal exteriors, showing suborbicular 

 outline and ornamentation. 

 4. — ^Ventral interior, showing characteristic bilobed muscle 

 field. 

 Ordovician (Trenton), 3 miles S. E. of Cannon 

 Falls, Minn. Cat. No. S 811. x 2.67. 

 7, 13. — Dorsal and ventral views of the exterior of Sarde- 

 son's holotype. 

 Ordovician (fucoid bed), Ellsworth, Wis. Cat. 

 No. S 935. x2. 



Dalmanella meeki (Miller) 



10,20,21. — Posterior, ventral, and dorsal exterior views, 

 X 1.5. This transverse type of shell strongly resembles 

 Bancroft's Onniella. 



23, 24. — Dorsal interiors, showing age variations. Fig. 23 

 portrays the younger shell, with its more slender car- 

 dinal process having a lobed myophore, indistinct ad- 

 ductor impressions, and bladelike brachiophores with 

 little adventitious thickening. The other shell shows 

 a prominent thickening of the cardinal process, with 

 some development of adventitious testaceous matter 

 on the inside surface of the brachiophores, and the 

 adductor impressions are more distinct, x 2. 



33. — Ventral interior, showing well the dental plates and 

 deep crural fossettes. Notice that the musculature 

 varies from that usual in Dalmanella rogata and allies 

 in not being lobate in front and in having the adduc- 

 tor track approximately the same length as the diduc- 

 tor impressions. The "meeki" type of Dalmanella 

 may be referable to Onniella when that genus has 

 become better established and its lineage put on a 

 substantial basis, x 2. 

 Ordovician (Richmond), Hanover, Ohio. Cat. No. 

 S855. 



Figs. Dalmanella ignota (Sardeson) 



19. — Internal mold, showing musculature. Adjustor scars 

 and elongate diductor impressions visible enclosing ad- 

 ductor impressions. Such a muscle pattern could have 

 produced that of Rhifidomella by expansion of the 

 diductor impressions to a semiflabellate outline. 

 Ordovician (Wykoff), Spring Valley, Minn. Cat. 

 No. S 947. X 2. 



Dalmanella emacerata (Hall) 



22. — Ventral internal mold showing bilobate muscle area 

 and pallial markings. Cf. interior of Parmorthis, 

 pi. 21. 



Ordovician (Maquoketa), Granger, Minn. Cat. 



No. S 954. X 2. 



Dalmanella corpulenta (Sardeson) 

 25. — Ventral internal mold, showing lobate muscle-scars. 



X 1.5. 

 27, 29. — Dorsal interior and exterior, x 2. 



Ordovician (Richmond), Spring Valley, Minn. 

 Cat. No. S 867. 



Dalmanella tersa (Sardeson) 



26, 30. — Dorsal interior, showing brachiophores, and dorsal 

 exterior. This shell is plano-convex in profile and 

 the ventral diductor scars wrap around the adductor 

 impressions. D. tersa has all the characters necessary 

 to produce Rhifidomella. 



Ordovician (Richmond), Wilmington, 111. Cat. 



No. S 871. x2. 



Resserella canalis (Sowerby) 

 14. — Ventral internal mold, showing divergent pallial 



marks. 

 15,1 6. — Dorsal internal mold, and impression taken from 

 it. Note, in the latter, structure identical with that 

 of D. rogata (figs. 2, 31). 

 Ordovician (low. Longvillian, Kjxrina zone). Long 

 Lane quarries S. of Horderley, E. Shropshire, Eng- 

 land. Cat. Nos.S 21 14 (fig. 14) and S 21 15. x 2. 



Heterorthina praeculta Bancroft 

 17. — Ventral internal mold, x 1.5, showing p.iHial markings. 

 28. — Ventral internal mold, showing musculature, x 1.5. 

 32.- — Cardinalia of dorsal valve, x 4. Bilobed myophore 

 and cleft shaft clearly visible, also simple bladelike 

 brachiophore plates. 

 Ordovician (Marshbrookian, Wattsella zvattsi zone), 

 Horderley District, E. Shropshire, England. Cat. 

 No. S2116. 



228 



