522 F. M. MacFarLAnD, 
of epithelial gland cells. What its significance may be is at present 
unknown. 
Alimentary system. "Ihe mouth opening is surrounded by soft 
fleshy, glandular lips leading into a very short oral tube or vesti- 
bule. Within this the inner lip disc, covering the anterior opening 
of the pharynx, is seen. It is eircular in outline, with an elongated 
vertical opening. Immediately in front of this disc the epithelium 
develops a euticle which thickens as the disc is approached, and, 
upon it, becomes greatly increased and split up into a mass of den- 
sely set, hair-like processes, each one of which, in its basal portion 
corresponds in width to a single epithelial cell. The distal ends 
of these eutieular hairs are frayed and worn, and in some instances 
appear to be split into further fine terminal divisions. They reach 
a length of 0,4 mm, the basal diameter being 0,003 to 0,005 mm, 
the height of the cell produeing them reaching but 0,021 mm. The 
action of KOH causes the lip disc to fall apart completely, save at 
its peripheral portion, where the eutiele is continuous. This labial 
{ringe would completely cover the mouth opening whenever the cir- 
cular eonstrietor muscle of the lip dise is contracted. 
The pharyngeal bulb is very large, often making up from one- 
third to one half the whole bulk of the viscera. The mandibles are 
massive, amber structures, departing markedly from the usual type 
found in the Aeolidiadae. Their form can best be understood by a 
reference to Figs. 5 and 6 of Plate 31, which represent the outer 
and inner surfaces of the mandibles of Dirona picta, and to Figs. 17 
and 18 of the same Plate, which show similar views for Dirona 
albolineata. Instead of the usual relatively thin concavo-convex wing 
portion, with a thicker artieular region and a masticatory process 
in front, the wing here is thick and strong (w), its outer surface 
is convex, the inner surface convex dorso-ventrally, and somewhat 
concave in an antero-posterior direction. The right mandible is 
often slightly shorter than the left, though the difference is not 
very marked. In both species the wing region is of a light, trans- 
lucent amber color, while the hinge region and the grinding surface 
are of a very dark reddish hue. The outer surface of the wing is 
convex with a slight groove radiating from the hinge region in both 
species. Upon the convex, inner face a sharp longitudinal ridge in 
Dirona piecta (Pl. 31 Fig. 6) marks the dorsal boundary of the large 
ventral adductor muscles which are inserted upon the whole of the 
wing of the mandible below this line, while above it this space is 
