Larcal Stages of Trilohifes. — Beechev. 177 
agrees, as far as can be determined without seeing the origi- 
nal, with wliat is ]<nown of otiier speeies of the same genus. 
It i^robably belongs to a stage later than the protaspis. 
Matthew26 has carefully described some small cephala of 
CteiiocephdlKs (Jlai-feJla) mattheiiu', and Coitocorjiphe (Baili- 
ella) hdtJeiii, from the Cambrian of New Brunswick. The fact 
of their l)eing sejiarate cephala, transverse in form, and from 
2 to 3 mm. in length, is sutticient to show that they do not 
represent the youngest stages of these species. 
The immature examples of Af/iiosttts, Trinuclus, Arethusina, 
Parado.rides, Olenel/iis, CfeiiocepJidliis and Conocoryiihe, here 
briefly noticed are of great interest in a study of the ontog- 
eny of the various species to which they pertain. In the pres- 
ent paper, however, it is intended chiefly to establish the pri- 
mary larval characters of the trilobites, and therefore only the 
earliest stages are considered. Under the genera just men- 
tioned, the writer has endeavored to show that as yet their 
ontogeny cannot be traced as far back as the stage which has 
been defined as X\\e jn-ofaspi.s. Therefore, any general notions 
of first larval forms must at present be based on the genera ISol- 
eiiopleKra, Liosfraciis^ Pfijchopd ria, Sao, Triarfhrn.s^ Acidasp/s, 
I'roY'fii.s and DahiKi iiites. 
IV. Analysis of Variations in Trilobite Larvae. 
After taking a general survey of the earliest known larval 
stages of trilobites figured on plates VIII, IX, it is evident that 
an accurate and detailed description of any one would not ap- 
ply to any other except in certain broad characters. To formu- 
late a definition of the protaspis applicable to all, as has been 
done previously (p. 169), it is necessary to neglect or eliminate 
some rather striking cliaracters which should now be men- 
tioned. A few features thus omitted are consideretl as very 
primitive larval characters, while others are modifications in- 
troduced in higher or later genera through the operation of 
the law of earlier inheritance. 
From the best evidence now (»])tainable, the eyes have mi- 
grated from the ventral side, first forward to the margin and 
then backward over the cephalon to their adult position, 
thus agreeing with Bernard's conclusions.!- Therefore, the 
most primitive larvte should present no evidence of eyes 
on the dorsal shield, and naturally there w<ui]d be no free- 
