148 EDWARD PHELPS ALLIS, JR. 
parts, where necessary to designate them separately, being 
called the supralabial and the postlabial furrows. <A third furrow 
lies in the lower jaw immediately and hence superficial to 
the mandibular labial. It extends posteriorly as far as the 
ventro-anterior end of the postlabial furrow, but ends dorsal 
(oral) to that furrow, not running directly into it, the two fur- 
rows being confluent superficially, but distinctly separate in 
their deeper portions. This third furrow may be called the 
supramandibular furrow and the related fold the supraman- 
dibular fold, the term mandibular being avoided because the fold 
and furrow both lie external and hence anterior to the man- 
dibular labial, and the term premandibular not being used 
because it implies something belonging to a premandibular arch 
or region. The labial and supramandibular folds together, form, 
in the Plagiostomi, a single large fold which is usually but not 
always separated into dorsal (maxillary) and ventral (man- 
dibular) portions by a posterior continuation of the line of the 
angle of the gape. Two other furrows are usually found, one in 
each jaw, running forward (symphysially) from the line-of the 
angle of the gape, not far from its inner end. They are both 
short, and were apparently primarily simply creases in the 
dermis between the folds of the primary and secondary lips. The 
crease in the upper lip runs symphysially, diverging slightly from 
the line of the primary upper lip. The crease in the lower lip, 
in the few specimens I have examined, curves aborally and 
approaches the outer end of the line of the angle of the gape, thus 
circumscribing a small islet of dermis which lies immediately 
symphysial to the line of the angle of the gape and external to 
the primary lower lip; the islet accordingly belonging to the 
tissues of the secondary lip. These little furrows will hereafter 
be referred to as the maxillary and mandibular preangular 
labial creases. 
In Chlamydoselachus these several furrows are not well de- 
veloped, the supralabial and supramandibular furrows being 
simply creases in the dermis which do not run together posterior 
and internal to the hind ends of the labials. There is accord- 
ingly no postlabial furrow, and hence no labial fold, properly 
