[RAYMOND] PARALLELISM AMONG THE ASAPHIDÆ 117 
glabella short, and the suture intra-marginal, thus producing Megalaspis 
and Asaphellus. In the third line the suture remains marginal, but 
the dorsal furrows become obsolete, and the result is Hemigyraspis, 
a close parallel in its smoothness to Jsotelus and Asaphellus. 
Thus we have six genera of smooth trilobites, all belonging to the 
Asaphidæ, all similar in general appearance, but developed along sepa- 
rate lines and not closely related. These genera are Nileus, Hemigy- 
raspis, Megalaspis, Asaphellus, Brachyaspis, and Jsotelus. 
Following out the development of the first group, we find no con- 
necting link between Ogygopsis and Platypeltis, Callaway, unless it be 
the species described by Schmidt as Ogygia dilatata panderi, a form 
which is, unfortunately, known from only one imperfect specimen. 
It is evidently not an Ogygiocaris, and has a long glabella with glabellar 
furrows at the sides, a distinct but smooth axial lobe on the pygidium, 
and smooth pleural lobes. I have called this Homoglossa. It appears 
to be near Platypeltis, Callaway, which has the glabella extending to 
the front, no marginal depression along the borders, and a smooth 
pygidium, on which, however, the axial lobe is fairly prominent. The 
axial lobe of the thorax is narrow. From this it is only one step to 
Symphysurus, Goldfuss, this genus differing from the preceding princi- 
pally in lacking the genal spines. Through the broadening of the axial 
lobe and the flattening of the glabella and the axial lobe of the pygidium, 
Nileus, Dalman, was developed from Symphysurus, and we have a line 
parallel to that proceeding from Asaphus to Brachyaspis, the two 
groups being similar in their short, wide cephalons, incurved profile, and 
long glabellas, but radically different in their hypostomas. 
In the second line, Ogygia corndensis, which I have called Ogyginus, 
forms a link between the Ogygopsis-Ogygiocaris line, and Megalaspis, 
Angelin. Ogygia corndensis has an intra-marginal facial suture, a 
glabella flatter and shorter than in Ogygiocaris or Ogygopsis, and fewer 
segments showing in the pygidium. Ptychocheilus, Novak, if correctly 
described, is intermediate between Ogygia corndensis and Asaphellus, 
Callaway. Ptychocheilus, as described by Novak and by Brogger, 
has an intra-marginal facial suture, a distinct glabella and axial lobe on 
pygidium, and ribs on the pleural lobes of the pygidium. Asaphellus 
has the intra-marginal suture, a glabella so faint as to merge into the 
general surface of the cranidium, and a smooth pygidium, but retains 
the primitive narrow axial lobe and genal spines. It is, nevertheless, a 
close parallel to Zsotelus, and is not always readily distinguished from 
that genus, especially as the more primitive and phylogerontic species 
of Isotelus have a rather narrow axial lobe. 
Megalaspis could hardly have developed from either Asaphellus or 
Ptychocheilus, but its close relation to Ogygiocaris is shown in the fur- 
