250 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
shell is 3.5 mm. long as it lies in the matrix, but as the pygidium is 
somewhat bent under the body, the actual length is probably .5 mm. 
greater. The cephalon is 2 mm. long and 4 mm. wide (semicircular) 
and is bordered by a wide (.5 mm.) concave brim. The glabella is 
convex, abruptly elevated above the brim at the front, bounded at the 
sides by deep dorsal furrows which converge backward. Between the 
eyes the glabella is marked by a pair of deep glabellar furrows. Be- 
hind them, on the narrowest part of the glabella, is a median tubercle, 
and on each side at this point is an isolated basal lobe. In short, the 
glabella is like that of an adult specimen of Basilicus (Plate 1, fig. 1). 
The facial suture can not be made out with absolute certainty on 
these smallest specimens. On a specimen with the cephalon 1.75 mm. 
long it seems to be marginal in front, while on a finely preserved 
cephalon 4 mm. long (No. 37), it is certainly intramarginal (Fig. 1). 
The eyes in the smallest specimens are 
very large, and only about one half — 
their own length from the posterior 
margin. On a cephalon 2.25 mm. 
long, the eyes are 1 mm. long and 
each forms a semicircle, the palpebral 
lobes almost touching the glabella in 
front. The posterior corner of the eye 
is only .38 mm. from the posterior mar- 
gin of the cephalon. The eye is there- 
fore relatively much larger than in the 
Fig. a ae His Lae As adult, but no further forward. The — 
bce, MEF EoD Re BED growth after this stage is more rapid © 
intramarginal. The pygidium in front of the eyes than behind them, 
is incurved so that the posterior onda cephalon 2mm. long has the eyes 
part is not well shown. X 6. s 
M.C.Z. No. 37. still only 1 mm. long. | 
The thorax of the smallest speci- 
mens shows few peculiarities other than the narrowness of the axial 
lobe. The specimen which is 3 mm. long has the axial lobe .5 mm. 
wide, or .2 the total width of the thorax. | | 
The smallest specimen with a well-preserved pygidium is 3.5 mm. 
long, and the pygidium is 1.25 mm. long and 2.5 mm. wide. ‘The | 
end. There is a narrow concave border, and the axial lobe reaches 
to and overhangs this border. The pleural lobes are convex, somewhat 
triangular, and crossed by four pairs of furrowed ribs. The axial | 
