
OF TRISTICHOPTERUS ALATUS. 393 
deeply imbricating—the exposed area being smaller than that which is over- 
lapped. The exposed surface is ornamented by very fine closely-set raised 
strie, often interrupted, and branching and anastomosing; their general 
direction is from before backwards, though they are usually seen to converge 
slightly towards the median line of the scale. On very close examination these 
strie may frequently be observed to be decussated obliquely by still more 
delicate lines, seen in the intervals between them, and which seem to radiate 
from the central point of the scale. The covered area is very minutely granular, 
a concentric linear arrangement of the granules being also usually to be 
observed. The impression of the under surface of a scale, in one specimen, 
shows evidence of a small elevated central boss or elevation. The scales of 
the lateral line seem to be perforated by a slime-canal, and to be slightly 
notched posteriorly. 
Conclusion.—The structural characters of 7ristichopterus, as far as they have 
as yet been ascertained, may be summed us as follows:— 
Body slender, elongated; scales cycloidal, thin, imbricating, delicately 
striated. External bones of the head sculptured; cranial roof bones united 
into a buckler of two principal parts, anterior and posterior; snout depressed, 
rounded; orbit placed far forward; a large preopercular plate covering the 
cheek in front of the well-developed operculum and suboperculum, as in the 
Saurodipterini. Gape extending far back; maxilla narrow, closely united 
internally to the bony palate; mandible stout ; jugular plates two, narrow; no 
median or lateral jugulars. Teeth in both jaws conical, sharp, slightly incurved, 
of different sizes; the larger teeth having the dentine thrown internally into a 
few simple folds at the base, which is also fluted externally. Vertebral column 
with ossified centra, attenuated posteriorly. Shoulder-girdle provided with 
interclaviculars; pectoral fins subacutely lobate; ventrals very slightly lobate. 
Dorsal fins two, placed far back and opposite the ventrals and anal respectively, 
the posterior dorsal and anal being each supported by three prominent inter- 
‘spinous bones. Caudal intermediate in general form between the heterocercal 
and diphycercal type; large, pointed above and below; the rays affixed to extreme 
termination of body-axis projecting beyond the line of the nearly vertical 
posterior margin of the rest of the fin. Rays of all the fins slender, articu- 
lated, closely set, overlapping their supporting ossicles ; fulcral scales absent. 
This assemblage of characters renders it evident that T7istichopterus has, 
as stated in the introduction, no affinity with Dzpterus, nor any special relationship 
with Celacanthus, but that, on the other hand, its place in Professor Hux ry’s 
classification of the Crossopterygian Ganoids is in the cycliferous division of 
| his family of Glyptodipterini. This group may, however, be very advan- 
-tageously subdivided, as there are structural differences between some of its 
| members, which, as it seems to me, are of importance enough to rank as family 
