105 



Among the Acrotheles there are several types of sculpturing of the 

 surface of the valves. The most characteristic is that of fine, short, 

 irregular wavy ridges, such as are found in A. Matthewi and A.granulata, 

 Another type is represented in A. proles, A. gamagei and A. cf. coriacea 

 wherein the ridges become more regularly concentric ; the valves in this 

 group are larger, and the ventral less selliform than in the precet-ding 

 one. White's description of A. subsidua would indicate that there is a 

 third style of ornamentation in the latter species, in which the surface is 

 papillose, yet with concentric lines of growth. 



From the time of its sudden appearance in the base of the Upper Ornamenta- 

 Etcheminian group, Acrothele continues to be common until we pass the 8 J^" a ce erf the 

 Lower Paradoxides beds ; from this point upward they are rarely met v& l ves i n this 

 with in Eastern Canada. It is thus in Canada apparently more limited in 

 range than Acrotreta, which extends up into the Ordovician. Its range 

 also differs from that of Acrothyra, which is a common genus in the Lower 

 Etcheminian, can be found even as far down as the Coldbrook, and also is 

 present with Acrothele in the Upper Etcheminian, but hardly invades 

 the Protolenus fauna ; where, as well as in the Lower Paradoxides beds, 

 shells of Acrothele are common. 



Neither in Eastern Cana la nor in Scandinavia do we find any Acrothele Range of the 

 reported from the Upper Cambrian, but in these countries the fine dark f^Jgj^ 

 ocean muds that were then accumulating were not favourable to the Canada, 

 .growth of Acrothele. Lindstrom however reported an undescribed 

 species from the Ceratopyge limestone (equivalent to the Trunadoc 

 Group of Wales) and from the occurrences in Bohemia and western 

 North America it would appear that the genus extended up into the 

 Ordovician or at least to its borders. 



LEPTOBOLUS, Hall. 



At several horizons in the Etcheminian terrane we have met with small Characteris- 

 Brachiopods which seem to agree with Hall's genus above cited better 

 than with any other. Such forms have usually been included in Lingu- 

 lella, but in addition to their minute size they are separated from that 

 genus by important characters. 



These little shells have thin test, weak umbones; vascular trunks are 

 s tuated near the lateral margins, and both the central and lateral muscle 

 in both valves are advanced far toward the front of the valves. They are to 

 be found both in sandy and muddy layers often mingled with Lingulella, 



*BuU. U. S. Geol. Surv. No. 30, p. 40. 



