098 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 Tennesseeze (‘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. 
«« 8, View of the side, exhibiting the dental elevations on the superior edges of the arm-bearing plates. 
ARTICLE ITI. 
SUMMARY OF THE DISTRIBUTION OF ORDERS, GENERA, AND SPECIES, IN THE NORTHWEST.* 
LOWER SIL. UPPER SIL. DEVONIAN. CARBONIF. TOTAL. | 
ORDERS. 
Species. “onera Species bic oe Species Genera Species. Genera Species i° enera | 
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 L 1 1 22 10 
Heteropoda, 3 2 1 1 Ei 1 5 4 
Pteropoda, “ 2 1 it 3 1 
Acephala, . 8 a 1 L. 6 4 15 9 
Brachiopoda, . . 39 8 8 + 34 8 43 5 | 124 25 
Foraminifera, . . 2 ‘4 1 ui 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. Speci Species. Species. cies. Species. 
peter... hey 1 2 9 12 24 
Orthig ey 12 5 + 21 
Leptene, =. 95 15 1 16 
Strophodonta, . 6 6 
Cauqnewe, 5 SS 4 4 8 
Froquccug, . ss 16 16 
Pentamerus, . . . 2 1? 3 
Terebratula, . . . 1? 1 Z 8 12 
ALU P Eee: a 3 6 9 
Obolus, - 1 n 
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 :—Leptena 
sericea, Leptena alternata, Orthis testudinaria, Spirifer biforatus, Lingula quadrata, Pentamerus 
oblongus, P. levis, Porcellia ornata, Pleurotomaria lenticularis, Obolus Appolinis, Isotelus gigas, Meenus 
crassicauda, Ceraurus pleurexanthemus, and Chetetes lycoperdon. The remainder correspond with 
species of the Wenlock formation, several species, however, being common to it and the Devonian system. 
They are :—Catenipora escharoides, Favosites gothlandica, Favosites spongites, Porites pyriformis, Atrypa 
reticularis, Terebratula Wilsonii, Leptena depressa, Spirifer trapezoidalis, 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. 
