o 



THE FAUNA OP THE ST. JOHN GROUP. 153 



Besides these , two species of Linnarsson, Prof. W. C. Brogger has described a third, ' 

 which is a typical species, except that the pygidium referred to it is comparatively too 

 narrow in the rachis. Judging from the Acadian species of this genus, another pygidium 

 figured (fig. 9) would belong to this species. 



In this genus, as in the preceding (Ptychoparia), there appear to be clear indication of 

 sexual distinctions which are of such a nature as to lead to the founding of different 

 species upon the differences which exist. In so far as these differences apply to the 

 Acadian species, they will be described on the succeeding pages. 



In the Acadian species, the most obvious distinctions between the broad and narrow 

 forms of the several species are that the former has a shorter and more conical glabella, the 

 rachis of the thorax has a greater proportionate width, and the pygidium has a shorter and 

 stouter rachis, with fewer joints both in the rachis and side lobes. Applying these charac- 

 teristics to the pygidia figured by Dr. Brogger in the memoir cited," the lower figure would 

 represent the pygidium of fig. 8 which aj^pears to be the broad form S. alutacea, and in 

 Angelin's "Palœontologica Scaudinavica,"the pygidium referred to Soleiiopleura holometopa, 

 would conform more nearly to the requirements of such a form as S. brachymetopa, and 

 vice versa. These two species of Angeliu are given the same range in the Paradoxides 

 beds of Sweden and Norway and probably occur together. 



The accepted characters of Solenopleura, as defined by the Scandinavian palœoutolo- 

 gists, may be gathered from the writings of G-. Linnarsson and "W. C. Brogger, and from an 

 earlier note of J. G. 0. Linnarsson, ^ where, in describing a species of this genus under 

 Conocoryphe, he says : — " It has fixed cheeks almost as high as the glabella, has a deep 

 dorsal furrow, a tubercle on the neck ring and other characters of Solenopleura." He 

 compares the pygidium to that of S. hravhymetopa, saying that it has four ribs on the side 

 lobe, and stating that the three ribs ascribed to S. bruchymetopa are plain ribs, while there 

 is really another obscure one behind these. This would bring the number into accord 

 with those of the narrow form in the Acadian species of Solenopleura. . 



Solenopleura Eobbii (Plate II, figs. 3 a to I and figs. 4 « to e.) 



ConocephuUies Robbii, Hartt (1868). Acad. Geol. 2nd. Ed. p. 648. 



C. formosus, " " " " " " 654. 



C. Orestes, " " " " " " 649, fig. 225. 



C. Thijrsites, " " " " " " 653. 



C. Hallii, " " " " " " 654 



Ptychoparia Robbii, Walcott (1884). U. S. Geol. Surv. Bull. 10. p. 36. (PI. VI, fig. 1). 



P. Robbii, \^r. formosus, Walcott. U. S. Geol. Surv. Bull. 10. p. 3t. (PI. VI, fig. la). 



P. Orestes, " " " " " " " 39. (PL V, fig. 3 a). 



P. Orestes, var. Thyrsites, " " " " " " " 40. (PI. V, fig. 2). 



P. Orestes, var. Hallii, " " " " " " " 40. (PI. V, fig. 3). 



' Om Paradoxides skifrene ved Krekling (1878) p. 51. Tab. iii. figs. 8 and 9. 



- Om paradoxides skifrene, etc. 



' Om Vestergotlands Cambriska and Siluriska aflagringer (1869) p. 72. 



Sec. iv, 1887. 20. 



