F. B. Cowper Reed— Blind Trilohites. 503 



(Ang.) from Dalecarlia, is a blind genus, but incompletely known. 

 Tornquist ^ describes it from the Leptcsna Limestone. 



The two genera, Conophrys (Callaway)2and Shumardia (Billings),^ 

 may be larval forms. Both are blind. Brogger* has suggested 

 that the species Conophrys pusiila (Sars), from the Ceratojyyg.e beds 

 of Sweden, may be the young of Ceratopyge forficula. The only 

 known British sj)ecies is Conophrys salopiensis (Callaway) from the 

 Shineton Shales. 



The type species of Shumardia is Sh. granulata (Billings) from 

 Point Levis, Quebec. Sh. glacialis (Billings) seems generically 

 distinct. 



Origin of Blind Forms. 



We have now passed briefly in review all the known blind forms 

 of trilohites, and we see that they fall into two natural divisions, of 

 which the first group comprises those in which eyes are not present 

 because of the low phylogenetic and morphological rank of the 

 genera in question, as their general structure and stratigraphical 

 appearance indicate ; and the second group includes those which are 

 generically identical or closely allied to forms possessing eyes, are 

 of high phylogenetic rank, and have lost their visual organs by 

 a secondarj^ modification, presumably as a result of adaptation to 

 special conditions. In brief, the first group may be called the 

 " primitive group," and the second the " adaptive group." As was 

 mentioned early in this paper, the absence of the compound eyes, 

 which are present in the majority of trilohites, marks a larval stage 

 in the ontogeny of higher forms corresponding with an adult 

 condition in a large proportion of Cambrian genera and species. 

 The phylogeny correlates so completely with the ontogeny that we 

 can have no doubt that we have found the clue to the puzzling 

 question of the meaning of blind trilohites. 



Classification. 

 The folio v^ing table shows these two divisions of blind trilohites : — 



Group 1. — Primitive Forms. 



Range. 



Agnostus (Brong.) ... ... ... ... Cambriau — Ordovician. 



Microdiscus (Emmons) ... ... ... Cambrian. 



Trinucleus (Lbwyd) ... ... ... ... Ordovician. 



Ampyx (Dalm.) ... ... ... ... Ordovician^Silurian. 



Dionicle (Barr.) ... ... ... ... Ordovician. 



? /Sato'iff (Wyv. Thomson) Ordovician. 



JSndymioiiia (Billiugs) ... ... ... Ordovician. 



Tiresias (McCoy) ... ... ... ... Ordovician. 



Conocoryphe, s.str. (Corda) .., ... ... Cambrian. 



Ctenocephalus (Corda) ... ... ... Cambrian. 



JSrinnys (Salter) ... ... ... ... Cambrian. 



1 TJndersokn. ofv. Siljans. Trilob. Svensk. Geol. Undersokn., ser. C, No. 66 

 (1884), p. 89. 



2 Callaway, Quart. Journ. Geol. Soc, vol. xxx (1874), p. 196 ; ibid., vol. xxxiii 

 (1877), p. 252. 



3 Pal. Foss. ^Canada, vol. i (1862), p. 92. 

 * Die Silur. Etagen 1 and 2, 1882, p. 125. 



