1896. ] NEW YORK ACADEMY OF SCIENCES. 159 
(B). Notochordal area and vertebral arches, NC. NA, HA, HS. 
(C). Supporting elements of the dorsal and of a pelvic fin, 
DENCE. VG: 
(A). VENTRAL ARMORING. 
There is little difficulty in identifying the typical plates of the 
ventral armoring, and in the accompanying figure, Pl. VIIL., 
Fig. 2, these have been arranged in approximately their natural 
relations. 
Of the Anterior Ventrals the fossil exhibits but a single plate, 
the left, Pl. VII., AV; this is shown in visceral aspect, its anterior 
margin broken and weathered. Its lateral margin, like that of 
Coccosteus, as described by Traquair,* and like that of Dinich- 
thys terrelli,as recently shown by Wright (op. cit.) is the thicker; 
and along this margin, which, by the by, is relatively wider and 
Jess incurved than in D. terrelli, pass well-marked parallel striz. 
The opposing margin of the plate is thinner, and shows little 
trace of encircling striz, although the weathering of the surface 
may possibly account for their absence. Vascular canals (Hav- 
ersian), rendered more conspicuous by the weathered surface, 
pass directly into the plate in its antero-lateral region; from 
this center they diverge radially, and become most conspicuous 
as open furrows in the thinner peripheral parts. The plate’s 
elongated candal end seems especially thin where it overlaps the 
left posterior ventral (Cf. Pl. VIII., Fig. 2, LPV). 
The Posterior Ventrals are both shown in the fossil, Pl. VILI., 
RPV,LPV. They are seen in visceral aspect, and appear to 
occupy very nearly their normal relations. Portions of these 
plates have been lost, but their structure is admirably preserved. 
The margins of the visceral surface are marked by concentric 
striz, which as in all the derm plates of Arthrodirans may be 
regarded as rings of growth. The focus of the vascular canals 
is prominent in the middle region of the plate, their radiating 
tubules becoming most conspicuous peripherally. The middle 
region of the left posterior ventral has been detached, but in 
such a way that a portion of its outer (surface) layer has been 
left in position. This fragment demonstrates clearly that the 
surface of the ventral armor in this, if not in every species of 
Dinichthys, was tuberclated. These tuberculations are fine, 
closely arranged, and project little above the surface; they form 
an encrusting superficial layer and, as the specimen indicates, 
separate readily from the underlying table of the plate. On this 
account it is possible that the dermal plates of Dinichthys terrelli, 
intermedius and curtus have always appeared to have been lack- 
* Traquair, Ann. Mag. Nat. Hist. [6] Vol. V., (1890), pp. 125-136. 
