MUSEUM OF COMPARATIVE ZOOLOGY. oe 
the middle. The glabella is marked by three pairs of shallow furrows, with 
perhaps a fourth scarcely discernible pair. The second and third pairs are not 
seen to meet across the median line; but owing to the position of two very low 
and rather indistinct tubercles, one anterior and one posterior to the first or 
posterior pair of furrows along the median line, these furrows seem to meet in a 
curve bending slightly backwards along the middle of the glabella. The palpe- 
bral lobes are large and prominent, beginning a little anterior to the third pair 
of furrows, and curving around to within a very short distance of the exten- . 
sion of the occipital furrow across the cheeks. The curve along the anterior 
border of the head is regular. A shallow groove runs within a short distance 
of the anterior border, gradually becoming deeper and broader and receding 
more from the border on the sides of the head, so that the rim here becomes 
broader. A faintly discernible shallow pit near the anterior extremity of the 
glabella may in this case be only accidental. 
Paradoxides tenellus, Billings, is in size like this species, but otherwise 
very distinct. It is interesting to find a Paradoxides in the Olenellus Cam- 
brian, since its occurrence there diminishes the importance of the Paradoxides 
Cambrian as a Paradoxides division. 
Locality and position.— Station No. 2, North Attleborough, Mass., Cam- 
brian, one specimen. 
22. Ptychoparia mucronatus, sp. n. 
Plate II. Fig. 21. 
Glabella in small specimens very convex, the degree of convexity decreasing 
with the increase of size; general form oval, the anterior part becoming some- 
what narrowed. The occipital furrow is always well defined. There are three 
pairs of glabellar furrows. These vary greatly in distinctness, being as a rule 
less prominent in young individuals and more marked in large specimens, 
The anterior pair is also usually much less distinct than the other two. The 
occipital ring is well rounded, except where interrupted by the nuchal spine, 
which is generally present, but usually small, being a mere terminal tubercle 
directed backwards and often more prominent in young specimens than in 
older individuals. From this are all variations to that of a moderate-sized 
spine. In one specimen, a fragment, the head of which may possibly have 
been 14mm. long, the spine extended for a distance of 3.2mm. beyond the 
general outline of the occipital ring, the base being broad, narrowing suddenly 
to ashort slender spine. Many large specimens are found in which this nuchal 
spine is not seen. Examination, however, always indicates that in these cases 
the posterior extremity of the occipital ring has been injured, so that the ab- 
sence of a nuchal spine cannot be definitely asserted. They agree perfectly in 
every other respect with the spined forms. Considering that we have positive 
evidence of large forms with spines, the absence of the same in specimens all 
apparently more or less injured seems to mean little. One specimen 15mm. 
