15^ Tlic Life-Hidury of Sj^irifer hevis. 



tinct imbrication of the concentric stria? ; in the fewer plica- 

 tions, which resemble rather one broad fold on each side of the 

 sinus than plications, and these rarely reach the beak ; the 

 hinge-line is shorter, giving a shorter and rather high area, 

 and the rounding of the lateral margins leads to the cbaracter 

 observed in Icevis, and other smooth forms — of a sudden curv- 

 ing of the strife at the extremities. 



This ajjpears to be the type of the ;S'. Icevis, H., of the Port- 

 age, and iS. curvatus, and especially glabe?-, Martin, of the 

 foreign Devonian and Carboniferous ; but here in the Niagara 

 it is closely associated with S. crispus, may be readily con 

 founded with it, and series of specimens connecting the two 

 forms can be made so complete tlnit theoretically we may pre- 

 sume the two are but varieties ; but we must note particularly 

 that the size of each of these Niagara species is very small com- 

 })ared with either ;S'. Icevis or ^S'. glaber. 



Spirifei' sulcatum, Hisinger, is a name applied to specimens 

 on the other side the Atlant'c, which undoubtedly are but 

 varieties of the typical form criapris, His., of which the pecu- 

 liarities are a greater extension of the hinge-line, an increase in 

 the number and abruptness of the plications, and a lower and 

 more extended hinge-arfta, and with this, a less prominent beak. 



In this country (and perhaps also in Britain and Europe), 

 some of the specimens identified and described as S. sulcatus, 

 His., are undoubtedly quite distinct from the grouj) of which 

 S. crispus, His., may be taken as the type. 



If we take, then, the median form of ;S'. crhpus, Wis., of the 

 Niagara as type, we see three distinct varieties : 



1st. S. crispus, His., with its rounded plications, three or four 

 at least on each side of the median sinus, short hinge-line, and 

 shape rather broader than long ; a moderate beak ; area mode- 

 rate but well defined, and not extending to the extreme lateral 

 margin of the shell. 



2d. S. hicostatus. Con., (and some specimens of cris'pus, Plis., 

 the var. simplex of Hall,) in Avhich the beak is prominent, the 

 breadth nearly equal to the length, the surface either quite 

 smooth, or with but one or two plications on each side of the 

 sinus, and these not reaching to the beak, and, when present, 

 the plications are broad and only slightly elevated folds; the 



