422 L. D. BIRLlNCi CAMBRIAN AND ORDOVICIAN RRACHIOPODA 



variety, and the maornitiKle of its geographic range. The present report 

 is hased on tlie study of 44 genera, 15 subgenera, 477 species, and 51) 

 varieties of Cambrian Brachiopoda, and 3 genera, 1 subgenus, 42 species, 

 and 1 variety of exclusively Ordovician Brachiopoda from 1,460 localities 

 within the national boundaries of 16 countries. The United States is 

 represented by collections from 28 States, Canada by localities in eight of 

 her provinces, and among tlie continents of the world Africa alone is 

 unrepresented. 



The sediments wci-c disidcd into three classes (limestone, shale, and 

 sandstone) and tiic following tables were prepared: (1) By genera and 

 subgenera, giving the number of species of each identified from the dif- 

 ferent sediments f (2) by genera and snbgenera, listing only those groui)s 

 which appear to be confined to one type of sediment and giving the 

 number of species of each and the number of localities from which tliey 

 have been identified; (3) by types of sediment, classifying the mutual 

 relationships between the several horizons of species occurring more than 

 once in the same section; (4) by character of gradation shown between 

 the horizons of all species occurring more than once, and (5) by three 

 arbitrary groups, giving the number of localities and the number of 

 species per locality in each of the three classes of sedinu'ut. 



Previous Work 



Foremost among previous investigations of a similar character is the 

 exhaustive work of Bigsby.* Based on (a) general divisions into cal- 

 careous and non -calcareous sediments and (h) minute discriminations, 

 recognizing 10 or 12 different types of sediment, his results can not bo 

 directly compared with those in this papur, but the following (igui-cs may 

 l)e of interest: "The calcareous or deep-sea sediments are much more 

 fossiliferous than the arenaceous oi' shallow bottoms, being as eight to 

 one I 823 to 102 (page 264)] in Xew York and two to one | 1.003 \n 724 

 (page 261) I in Wales" (page 260). "Most of the genera (d' r)ra<hio])oda 

 furnish examples of arenicolous and argillicolous species" (i)age 262). 

 "Of 254 species of Brachiopoda in Xew Yoi'k. of known matrix, only 24 

 [24 out of 237 (page 264)] are found in non-calcareous sedinuMits: 

 whilst in Wales the distribution is much more general, there l)eing 207 

 appearances in the beds just spoken of. against 30!) in the limestone 

 rocks" (page 262). Dividing the sediments into grou|)s necessitating a 



," A preUnilnary draft of this tnlde was inntrporatod in ('aniltrinn nracliiopoda. Mt>no;;r. 

 f.'S. r,e<»l. Surv«\v. vol. U. pt. I. lOll!. by Charlos I>. Walcott. p. KJo. 



* ()uart. .lonr. fleol. S<k'. Ivondon. vol. l.'.. ISHO. pp. I'.'d -.'{:{."( : Tart III. — An in«piiiy 

 into the siMlimcntary and otlior c>.xtfrnal relations of the Paleozoic fossils of the State of 

 New York. 



