PLATE 29 



Figs. Pionodema cf. conradi (N. H. Winchell) 

 1 . — ^Thin section, showing endopunctas. It is to this type 

 of internal shell perforation that we restrict the term 

 endopunctje. The section figured is a portion of the 

 shell shown on pi. 23, fig. 9. 

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

 No. S 1367. xca. 12. 



Aulacophoria keyserlingiana (De Koninck) 

 2,5,10. — Ventral, dorsal, and lateral views of complete 

 individual. Anterior like that of Schizofhoria, but 

 prominent fold and sulcus a divergence toward 

 Enteletes. 

 Carboniferous, Welton, England. Cat. No. S 1924. 

 xl. 



Hesperorthis laurentina (Billings) 



3. — ^Thin section, showing deltidium in place. Cf. 

 Silurian, Anticosti. Cat. No. S 2221. x 4. 



fig. 8. 



Conchidium biloculare Linnaeus 



4.- 



-Cross section of shell, showing deltidium in place. 

 In an anterior direction from the position of this sec- 

 tion (which is near the beaks) the deltidium becomes 

 a flatly concave plate. In this figure the sides of the 

 deltidium have been broken from the walls of the del- 

 thyrial cavity. In Conchidium the deltidium was 

 evidently a pedicle sheath open at the posterior. A 

 similar structure appears in H arfidium. See t. fig. 25. 



Silurian (Gotlandian), KJintehamn, Gotland, 



Sweden. Cat. No. S 1872. x 3. 



Stricklandia davidsoni Billings 

 —Section showing duplex spondylium and cardinalia. 

 Notice also lateral elevated plates on cardinal region 

 of dorsal valve. 

 Silurian (Jupiter River), East Jupiter Cliff, Anti- 

 costi. Cat. No. S 1898. x5. 



Parastrophinella reversa (Billings) 



—Section showing spondylium and cardinalia. Note 

 prominent dorsal plates and folded or duplex charac- 

 ter of alae in dorsal valve. 

 Silurian, base of White Cliff, Cape Eagle, Anti- 

 costi. Cat. No. S 1607. x4.5. 



Fics. Vellamo diversa (Shaler) 



8. — Section showing spondylium. Note thickening in 

 umbo-lateral chambers (cf. fig. 14). Note deltidium 

 built against delthyrial edge and strengthened by 

 shell deposit on sides of delthyrial cavity (T = trace 

 of tooth showing as an irregularly oval spot). x4.5. 

 14. — Section showing umbonal chambers completely filled 

 by adventitious shell. Note thickened deltidium and 

 callus spread on inside of delthyrial cavity, x 3. 

 Ordovician (Ellis Bay), W. side Ellis Bay, Anticosti. 

 Cat. Nos. S 2222a (fig. 8) and S 2222b. 



Liocoelia proxima (Barrande) 

 -Section showing spondylium and cardinalia which 

 strongly suggest Camerofhoria and the rhynchonellids. 

 See t. fig. 36. 

 Silurian (Etage Eej), Kolednik, Bohemia. Cat. 

 No. SI 696a. x4.5. 



Pentamerus aflf. oblongus Sowerby 

 1 1. — Section showing duplex spondylium and characteristic 

 dorsal lamella. 

 Silurian (Jupiter River), Belle River, Anticosti. 

 Cat. No. S 1819. x ca. 4. 



Billingsella lindstromi (Linnarsson) 

 12. — ^Tangential section showing fibrous structure. Frag- 

 ment of shell taken from specimen figured on pi. 1, 

 fig. 27. 

 Mid. Cambrian (Paradoxides zone), Westrogothia, 

 Lovened, Sweden. Cat. No. S 16a. 



Billingsella coloradoensis (Shumard) 

 1 3. — ^This tangential section was figured by Walcott (Camb. 

 Brach., p. 299, fig. 5) but the greater magnification 

 used by him did not reveal the true structure. There 

 are no punctse in Billingsella and the section shows 

 the fibers. See fig. 12. 

 Up. Cambrian, Morgan Creek, Burnet Co., Texas. 

 U. S. Nat. Mus. 



252 



