428 L. D. BrRLIXC (AMIJRIAX AND ORDOVICIAN BRACHIOPODA 



Of the twelve genera and subgenera represented by single species in 

 single faunules, 7 CM?eur in limestone, 2 in shale, and 3 in sandstone. For 

 tlie fourteen more widely distril)uted genera the following discussion of 

 the results embodied in the table may l)e of interest: One genus is eon- 

 fined to shale, but the two species of which it is composed are confined to 

 single faunules. The apparently isolated examples of Bicki and Eostro- 

 phoinena from limestone might likewise be dismissed if it were not for 

 the inclusion of SiphonotretaJ a genus which is typically represented by 

 two species from 23 localities. Three genera are thus not only confined 

 to limestone, but are represented, in the case of Bicm and Siphonotreta at 

 lea^t. by a sufficient number of localities to render noteworthy their 

 affinity for calcareous sediments. The genera and subgenera which ap- 

 pear to be confined to sandstone have been recorded largely from single 

 geologic provinces; but these regions have been extensively studied and 

 the figures are large enough to be convincing, if indeed they do not prove 

 a marked preference on the part of several of these generic groups for an 

 arenaceous habitat. Thus ten genera and subgenera, represented in the 

 collections at our disposal by 19 species from 108 localities, appear to be 

 confined to sandstone. 



LiTIIOLOGIC, STRATIGRAPHIC, AXD GEOGRAPHIC EaXGE COMPARED 



Species common to different sediments are shown on analysis to ex- 

 hibit a more or less similar latitude in their stratigraphic range; to be 

 exact, 44 per cent of the species occurring in more than one type of sedi- 

 ment (141) have been identified from more than one of the three main 

 divisions (Lower, Middle, and Upper) of the Cambrian. 



By a similar analysis it can be shown that there is a still closer rela- 

 tionship between lithologic and geographic range. Thus of the 141 spe- 

 cies common to different sediments, 89 (or 63 per cent) have been col- 

 lected from more than one State, province, or country, the number of 

 such units ranging from 2 to 18, with an average of over 4 ; and of the 89 

 species just mentioned, 49 (or 55 per cent) appear to be common not 

 only to four or more of these artificial units, but also to separable geologic 

 provinces. 



' See the footnote to Fdphonoircia on the precedinic page. 



