F. R. Coicper Reed—Blind Trilobites. 505 



have been made, and that some alterations have been necessitated 

 by the revised nomenclature, such as in the case of Conocephalites 

 and the elimination of the genus Atops, upon which I have 

 commented above. 



Barkanbe's Group 1. — Genera of which all the known Species 



are blind. 



(«) Genera recorded in Bohemia. 

 Agnostus, Brong. Dindymene, Corda. 



Ampyx, Dalm. Dionide, Barr. 



Areia, Barr. Flacoparia, Corda. 



{b) Genera recorded in Foreign Countries. 

 Acontheus [=Aneucanthus), Angel. " Microdiscus, Emm. 

 Anopocare, Angel. Bathynotus, Hall. 



Eryx, Angel. Endymion, Bill. 



Isocolus, Angel. Shimiardia, Bill. 



Atops, Emm. Typhloniscus, Salt. 



Group 2. — Genera of which only some Species are blind. 



ia) Genera recorded in Bohemia. 



Camion, Barr. IUcbiius, Dalm. 



Conocephalites, Zenk. Telephus'^, Barr. 



Harpes, Goldf. Trinucleus, Lliwyd. 



[b) Genus recorded in Foreign Countries. 



Phacops, Emm. 



Geological Distribution. 



We must now consider the geological distribution of these blind 

 forms. Barrande (loc. cifc.) noticed that they were mostly confined 

 to the " Lower Sihu'ian," and in his summary (Suppl., vol. i, 

 pp. 155-162) he brought out the facts of their distribution by 

 means of ratios, showing that the largest proportion occurred in the 

 " Primordial Fauna," amounting to -296 of the whole number of species 

 of trilobites in Etage C, i.e. eight species out of the twenty-seven 

 recorded from it. in his "Second Fauna" the proportion was less, 

 being only -2 of the whole, i.e. 25 species out of 127 ; while in the 

 " Third Fauna " only one out of the 205 species was known. The 

 decrease in the relative abundance of blind forms is thus very marked 

 as we rise in the stratigraphical succession. But out of the total 

 number of blind species in Bohemia about three-fourths occur in the 

 " Second Fauna." 



If we now turn to the list I have given of blind forms, and confine 

 our attention first to Group 1 — the primitive forms — we shall see that 

 their predominance in the Cambrian is plainly exemplified. Thus, 

 omitting those genera which for various reasons stated above are 

 doubtfully included in this group, or may possibly possess eyes or 

 be immature forms, we find there are eleven genera occurring in the 

 Cambrian, of which ten are peculiar to it and one ranges up into 

 the Ordovician. Nine genera occur in the Ordovician, of which 

 seven are peculiar and one ranges up into the Silurian. Only one 

 genus is known from the Silurian, and this is a survivor from the 

 Ordovician. In the Devonian there is only one, and that is doubtful. 

 As Beecher^ has shown in a diagram, the Hypoparia are more 

 1 Amer. Journ. Sci., vol. iii (1897), p. 182. 



