598 A. W. GRABAU LOWER ORDOVICIC FORMATIONS 



angustifrons Dalm., Cyrtometopus clavifrons Dalm., Illcenus cenlrotus 

 Dalm., and Amphion brevicapitatus Lamansky. Other species of these 

 genera also occur. All of the brachiopods continue upward from the pre- 

 ceding bed or the one before it, and the same may be said of the crinoids, 

 corals, and Bryozoa. On the whole, while all three divisions show rela- 

 tionship, B II ft and y are more closely related faunally, while B II a is 

 closely bound to the preceding horizons of B I. There is, however, an 

 absolute distinctness of species between horizons B II and B III, with 

 the exception of the Bryozoa. Of the 31 trilobites of Division B II, only 

 Piycliopyge angustifrons Dalm. is recorded from both B II and B III; 

 but, as Lamansky points out, under this name are included many distinct 

 mutations, which, when separated, would be found to be restricted to 

 distinct horizons. None of the twenty brachiopods found in B II pass 

 upward into B III, and the same is ti;ue of the 13 echinoclerms and of 

 the pteropods and cephalopods. Only among the Bryozoa seems there to 

 be a continuance of species, not only between B II and B III, but also 

 between B II and horizons above B III. Of the 12 species recorded by 

 Bassler from B II, 7, or 58. 33-^- per cent, occur in B III or in C. Two 

 of these range into the highest division of the Baltic series. Two species 

 are American, found here in the Lower Trenton. Either sufficient care 

 was not taken in the collection of the material on which Bassler based his 

 determinations or the Bryozoa are not such good horizon-markers as has 

 been assumed. 30 



The entire group B II is designated by Lamansky as the Megalaspis 

 group, 31 while the succeeding division, B III, is designated the Asaphus 

 group. This also consists of three divisions designated B III a, B III ($, 

 and B III y, respectively, by Lamansky. The first is characterized by 

 Asaphus expansus, A. lamanshii, etcetera; by species of Niobe, Illsemis, 

 Cyrtometopus, Metopias, and other trilobites. Among these, I litmus 

 esmarcTcii Sehloth. and Cyrtometopus affinis Ang., Amphion fischeri 

 Eichw., and Metopias pachyrrhina Dalm. range through all these sub- 

 divisions. 



B III a is also marked by the first appearance of Orthis calligramma 

 Dalm., which ranges through the whole division and is wide-spread in 

 the LTpper Ordovicic of England (Caradocian), and the equivalent horizon 



30 See also Axel Borns' criticisms of Basslcr's Bryozoa lists. Centralblatt fur Min. 

 Geol. u. Pal., 1913, p. 712. It should be remarked in justice to Bassler's work that the 

 material on which he based his determinations was brought together by several col- 

 lectors, and that he can not be held responsible for misplacement of horizons. 



31 Raymond has proposed the name -'Walchow formation" for this division, but in- 

 cludes with it Division B I and Division B III a of Lamansky. This last is not justified, 

 owing to the evidence of a break between B II y and B III a, and especially because of 

 the almost complete change of fauna as recorded by Lamansky. 



