NO. 1395. CAMBRIAN BRA CHIOPODA— WA L CO TT. 275 



occupied by the diductor iniiscle scars, and the two hiteral divisions arc 

 continuous with the ridges representing the casts of the main vascular 

 sinuses. I have been unable to determine positively whether there is 

 a deltidium present or not. The delthyrium is clearly shown in sev- 

 eral specimens. Casts of the interior of the dorsal valve from New- 

 foimdland show the presence of crural plates that extend to the bottom 

 of the valve; also short, but very definite, crura and small depressions 

 beside the latter for the reception of the teeth of the ventral valve. A 

 cast of the ventral valve shows that the ventral plates extend to the 

 bottom of the valve, and specimens from Sweden show that the dental 

 plates and a transverse arching ridge sharply define, in certain indi- 

 vidual ventral valves, the umbonal cavity. 



The average size of the specimens from Olands is about 5 by 6 mm. 

 One dorsal valve is 7 by 1> mm. 1'hose from Nunneberg average from 

 5 to () mm., with occasional shells 7 by 8. In Newfoundland great 

 numbers occur 4 by 5 nmi., but there are also examples having a 

 height of 10 mm., with a width of 12 mm. Doctor Matthew states that 

 the medium size of the shell is about 5 b}^ 6 mm. in the Acadian rocks. 

 Doctor Brogger mentioned an example from Toien, Vestfossen, 10.5 

 by 12.5 mm. 



I have noi attempted any detailed description of the species, as 

 it is so variable in form and surface markings. An attempt was 

 made to discriminate varieties in the material from Sweden and 

 Newfoundland, but there was such a gradation in all of the characters 

 upon which such differentiation might rest that it was finally aban- 

 doned. Doctor Matthew considers that he has reason for establishing 

 varieties among the New Brunswick forms. Whether these would be 

 of value if a large amount of material w^ere available for comparison 

 is doubtful. 



Dr. E. Kaj^ser^' illustrates a shell that is apparently identical with 

 O. (O.) lenticular is, which occurs in the sandstone at Tilcuya, Argen- 

 tine Republic, in association with Olenus, AgnosUm^ etc. He also 

 illustrates on Plate I, fig. 13, a dorsal valve of a small Ort?tis that in 

 many respects looks more like (). lenticularis than figs, 11 and 12. I 

 very much doubt if they represent this species; in fact Doctor Kayser 

 questions his identification by an interrogation mark. He says of the 

 shell: 



Another much smaller Orthis species occurs in the fine-grained sandstones of Til- 

 cuya, associated with Olenus, Agnostus, Arionellus, Theca, and Orthis saltensis, 

 which has just been described. The smaller Orthis species is transversely oval in 

 outline, with straight hinge edge, corre.sponding to the greatest breadth of the shell. 

 The ventral valve is moderately arched, the dorsal somewhat less. The surface of 

 both valves is covered with comparatively strong ribs, arranged in bundles. On the 

 middle of the ventral valve there is an especially well-marked rib or bundle of ribs. 



« Paleontographica, Primordiale und untersil. Foss. Argentenischen Kep'b., p. 9, 

 pi. I, figs. 11, 12. 



