146 TRANSACTIONS OF THE  [mMar. 17, 
BERGERONIA n. subgen. 
A better knowledge of the species Protolenus elegans makes 
it necessary to separate it from Protolenus paradoxoides by 
something more than a specific designation. The segment of 
the thorax of P. elegans, figured in the author’s paper, read 
before the Royal Society of Canada in 1893, was found in slaty 
rock, and had been flattened by pressure; for this reason it did 
not show the strong geniculation, which the pleurz in their na- 
tural form possess. A comparison of the pleural parts of 
the two species named above, show radical differences, and al- 
though the glabellas are similar, it seems desirable to mark the 
difference in other respects by a subgeneric name. P. elegans in 
the strongly grooved and geniculate pleurz, resembles Ptycho- 
paria (and Solenopleura but for the apical spines), while P. para- 
doxoides has the flat pleura, with diagonal furrow, characteristic 
of the Olenide. 
To the species elegans, which would thus become the type of a 
subgenus, should be added one which has been doubtfully ranged 
under Agraulos and Ellipsocephalus, but which now by its 
thorax, and the general contour of the head-shield, is seen to be 
congeneric with P. elegans; this is Hllipsocephalus (?) articeph- 
alus. 
In dividing off a new genus or sub-genus, it is customary to 
retain the species first described as the type of the old genus ; 
but in this case it would not be advisable to do so, because the 
second represents best the conception of the genus. P. elegans 
was described first, because the material for the elucidation 
of this species was most complete. To some naturalists Ber- 
geronia will seem only a subgenus of Protolenus; whether it be 
considered a genus or subgenus will depend upon the compara- 
tive importance assigned to the thorax, as contrasted with the 
glabella. Barrande, Salter and other writers on the trilobites, 
have considered the course of the dorsal suture, and the form of 
the pleura, its groove and facet, of great importance in determin- 
ing genera; the determination of the standing of Bergeronia 
will depend upon whether we assign the greater value to the 
pleural features, or to the form and relation of the glabella. 
It was probably because of the resemblance borne by the 
thorax of S? Howleyi of the Lower Cambrian of Newfoundland 
to that of a Solenopleura that Mr. Walcott ranged that species 
provisionally under this genus; but the author’s studies of the em- 
bryonic forms of Solenopleura and other Ptychoparida show that 
this species can hardly be included in that genus. For in Sole- 
nopleura the eyelobe, even in the youngest forms in which it can 
