June, 1916] The Ordovician-Silurian Boundary 331 



of Illinois, Tennessee, Missouri, Arkansas and Oklahoma. 

 The reasons for excluding the Anticosti series will be given 

 later. 



In these lists all forms of problematic origin, doubtful range 

 and uncertain relationships have been excluded. 



Of the 413 Maysville species, 58, or about 14%, lived on 

 into the Richmond. Nor are all species of generalized types 

 and long range, but we have among them such highly specialized 

 cystoids as Streptaster vorticellata, Agelacrinus cincinnatiensis 

 and Cyclocystoides magnus, while Bassler lists the starfish 

 Hudsonaster incomptus and Mesopalaeaster shafferi. Heter- 

 ocrinus juvenis and locrinus subcrassus represent the crinoids. 

 Eleven species of Bryozoa are common, ten of Brachiopoda, six 

 Pelecypods, ten Gastropods, four Ostracods, etc., etc. 



Of the 217 Richmond genera, 116 are common to the Mays- 

 ville. Of the 101 which are not, 68 occur below the Maysville, 

 leaving 33 genera which are really new. And these introduce 

 five new families, the Fenestellidae, Rhopalonariidae, Bato- 

 criniidae, Halysitidse and Loxonematidae. 



2. But contrast with this the fact that the Upper Medina 

 (Albion) and Clinton give 255 genera, only 82 of which have 

 been found in the Richmond, and of these 68 are long-ranging 

 groups, which came up from Pre-Richmond times, usually 

 Black River or Trenton. 



Of the 173 genera not common to the Richmond, 40 also 

 lived below the Richmond, leaving 133 as really new. And 

 these 133 new genera introduce 35 new families, the suborders 

 Larviformia and Sagenocrinoidea, the orders Madreporaria, 

 Diploporita and Streptophiuriae, and the subclass Hexacoralla. 

 Should we consider the Upper Medina alone the proportion of 

 new major groups would be still greater. 



Compared with the above record the innovations of the 

 Richmond seem almost lonesome, and the faunal break looms 

 up still greater when we consider that of all the Richmond 

 species, but one lone species, Halysites catenularia, occurs in the 

 upper strata. But more of Halysites presently. 



In comparing two faunas there is a difference of quality 

 as well as of quantity, and both are of conspicuous value in 

 comparing the Richmond and the Upper Medina-Clinton 

 faunas. 



