External Characters. 
148 
Most of the external features have already been briefly described 
in the last section. 
Fig. 32 (X circ. 2). 
Fig. 33 (x cire. 4). 
of Mordacia. 
Fig. 34 (x cire. 4). 
Figure 31 illustrates the 
Lateral view of skeleton of head 
region of Mordacia mordax. 
Latera] view of piston cartilage 
Ventral view of ditto. 
arrangement of the 
teeth in the suctorial 
funnel. It will be 
seen that the two’ 
dorsolateral maxil- 
lary teeth (Mx.Lam.) 
are rounded triangu- 
lar plates (shown 
only in outline) each 
bearing three curved 
cusps (black in the 
drawing), and that 
these two teeth, with 
the large semicircu- 
lar mandibular tooth 
(Mn. Lam.) bearing 9 
cusps) and two pairs 
of small lateral isola- 
ted cusps form an 
inner circular series 
of cusp-bearing lami- 
nae. Immediately 
external to this inner 
series is another and 
more regular con- 
centric series of cusp- 
bearing plates. As 
will be seen, these 
plates vary slightly 
in size, the dorsal 
being smaller than 
the ventral and each 
bear from one (dor- 
sally) to four (late- 
rally) cusps. Exter- 
nal to this outer concentric series on the anterior or dorsal side of 
the disc lie numerous small non-cusp-bearing irregularly-arranged 
platelets. 
As in figure 8, the cavity of the mouth is left unshaded. 
