598 DISTRIBUTION OF ORDERS, GENERA, AND SPECIES, 



The species resembles in some respects Synbathocrinus conicus (Phillips), but is easily distinguished 

 by the larger size of its basal plate, and the shortness of its superior plates. From the description of 

 Synbathocrinus Tennesseeee (Troost in MS.), it differs in several important characters, and occupies a 

 different geological position. 



EXPLANATION OF FIGURES. 



Fig. 7. a. Basal View, showing the tripartite character of the basal plate. 



" b. View of the side, exhibiting the dental elevations on the superior edges of the arm-bearing plates. 



ARTICLE III. 



SUMMARY OF THE DISTRIBUTION OF ORDERS, GENERA, AND SPECIES, IN THE NORTHWEST.* 



ORDERS. 



LOWER SIL. 



OTPER SIL. 



DEVONIAN. 



CARBONIF. 



TOTAL. 



Species. 



Genera. 



Species. 



Genera. 



Species. 



Genera. 



Species. 



Genera. 



Species. 



Genera. 



Crustacea(Trilobites) 



28 



12 







2 



1 



3 



1 



33 



14 



Crinoidea, . 



2 



2 







3 



3 



24 



9 



29 



14 



Cephalopoda, . . 



19 



8 











2 



2 



21 



10 



Gasteropoda, . . 



20 



8 







1 



1 



1 



1 



22 



10 



Heteropoda, . . 



3 



2 







1 



1 



1 



1 



5 



4 



Pteropoda, . . . 



2 



1 











1 ? 





3 



1 



Acephala, . . . 



8 



4 



1 



1 







6 



4 



15 



9 



Brachiopoda, . . 



39 



8 



8 



4 



34 



8 



43 



5 



124 



25 



Foraminifera, . . 



2 



1 











1 



1 



3 



2 



Polyparia. . . . 



1 



1 



11 



11 



22 



11 



12 



6 



46 



21 



THE GENERA OF BRACHIOPODA ARE DISTRIBUTED AS FOLLOWS : 





LOWER SIL. 



UPPER SIL. 



DEVONIAN. 



CARBONIF. 



TOTAL. 



GENERA. 



Species. 



Species. 



Species. 



Species. 



Species. 



Spirifer, .... 



1 



2 



9 



12 



24 



Orthis, 



12 





5 



4 



21 



Leptoena, .... 



15 





1 





16 



Strophodonta, . . . 







6 





6 



Chonetes, .... 







4 



4 



8 



Productus, .... 









10 



16 



Pentamerus, . . 





2 



1? 





3 



Terebratula, . . . 



1? 



1 



2 



8 



12 



Atrypa, 



3 





6 





9 



Obolus, • . . . . 



1 









1 



Lingula, .... 



5 



2 







7 



Orbicula 



1 









1 



Total Brachiopoda. 



39 



7 



34 



44 



124 



Of the species found in the beds of the Northwest, from the top of the upper magnesian limestone to 

 the base of the lowest sandstone, twenty-three have been identified with forms occurring in the Lower 

 Silurian strata of Europe. The following characterize the inferior system of both countries : — Leptaena 

 sericea, Leptsena alternata, Orthis testudinaria, Spirifer biforatus, Lingida quadrata, Pentamerus 

 oblongus, P. Isevis, Porcellia omata, PIcurotomaria lenticularis, Obolus Appolinis, Isotelus gigas, lllsenus 

 crassicauda, Ceraurus pleurexanthemus, and Cheetetes lycoperdon. The remainder correspond with 

 species of the Wenlock formation, several species, however, being common to it and the Devonian system. 

 They are : — Catenipora escharoidcs, Favosites gothlandica, Pavosites spongites, Pontes pyriformis, Atrypa 

 reticularis, Terebratula Wilsonii, Leptama depressa, Spirifer trapczoidalis, and Pentamerus galeatus. 



As might be expected, a much larger number corresponds with species occurring in the equivalent beds 

 of New York, Ohio, Kentucky, and Tennessee. At least forty-six have proved to be identical with species 



* Modified by additions and researches since the publication in the Proceedings of the American Association, 1851. 



