[DAWSON] FOSSIL SPONGES AND OTHER ORGANIC REMAINS 119 



ganic discs of pyrite, or may represent flattened organic bodies. In the 

 latter case, they may be germs or ova, or spores, or portions of some 

 complex vegetable or animal organism They recall the little spherules 

 described by Matthew as occurring in the Cambrian of New Brunswick, 

 and named by him Monadites globularis. 1 have not been able, however, 

 to detect any indications of connecting rods or stalks like those figured 

 by Matthew/ 



YI. OTHER ANIMAL REMAINS. 



The most important of these are the little l)rachiopods referred to 

 above : 



Obolella (Linnarssonia) pretiosa, Billings. 



Fig. 31. — Linnarssonia prêt iosa, Billings, a, natural size of medium specimens, 

 6, ventral, c, dorsal valve. 



These are very abundant on the same surfaces which hold the sponges, 

 and are usually replaced by pyrite, though sometimes appearing as mere 

 casts. They often show their interior structures as represented in Fig. 

 31. They aftbrd for the present the best evidence in relation to the geo- 

 logical age of the deposit, since the species is characteristic of the Sillery, and 

 the genus is a Cambrian rather than Ordovician one in Europe. For this 

 reason I quote here Dr. Hall's description, based on Metis specimens 

 submitted to him some years ago. I may add that Mr. Whiteaves, our 

 best Canadian authority, concurs in referring these shells to Billings's 

 species 0. pretiosa : 



" Shell small, subcircular or elongate transversely. Yal ves subequally 

 convex, the ventral beak erect, slightly projecting and perforated at its 

 apex. External surface covered with fine concentric lines, faint radia- 

 ting striae being visible on the interstitial lamella\ The interior of the 

 ventral valve bears a subtriangular or U'^^^'^ped ridge, the bî'anches of 

 which diverge anteriorly. The thickest portion of this ridge at the union 

 of the branches is penetrated by the foraminal tube. In front of the 

 foramen, and just within the cardinal line, on either side the axis of the 

 shell is a conspicitous tubercle or l)Oss. In the dorsal valve is a median 

 ridge, extending half the length of the valve, and from this two short 

 lateral ridges diverge, taking their origin at one-third the length of the 

 median ridge from the posterior margin." 



1 Transactions Royal Society, 1889. 



