from the Neighbourhood of Edinburgh. 267 
length of the fragment is 16 inches, and its greatest breadth 
8 inches; in front there are some mutilated and unread- 
able remains of the head extending back for about 6 inches ; 
but here a few doubly trenchant teeth of the well-known 
aspect and structure settle the question as to its being a 
Rhizodus. Behind these head-remains, and lying across the 
specimen, is a great part of a well-marked clay icle, resembling 
in shape that of /oloptychius and ornamented externally by 
Beceem ridges, furrows, and pits. The amount of it seen 
is 53 inches in length; it is overlapped in front by some por- 
tions of head- -bone, probably opercular ; above, it is broken off 
at the edge of the specimen; and below, its termination is 
not very distinct, though I am rather disposed to think that 
another portion of bone coming on here is the ¢nterclavicular. 
The posterior margin shows a shallow excavation, from which 
issues a pectoral fin, obtusely or oulediuely ’ lobate in shape. 
The “lobe” is 3 inches long by 1? broad ; it is fringed with 
rays on the upper and posterior margins, some remains of 
them extending also a little round on the lower. The most 
perfect rays are those on the extremity of the lobe, where 
3 inch of their length is seen ; they are slender, smooth, and 
very closely set; for an inch of their length they are unarticu- 
lated, after which transverse divisions are evident. 
Behind the remains of the head and pectoral arch the speci- 
men is covered by scales, which agree perfectly with those 
which we have been accustomed to refer to Rhizodus Hibberti. 
They lie for the most part undisturbedly zn stu, deeply im- 
bricating over each other, but, as usual, are mostly so split 
that only their internal str ucture, not their external sculpture, 
can be seen. One of these scales, just behind the upper end 
of the clavicle and pushed rather out of place, is seen to mea- 
sure 13 inch in length by 1} in breadth; on the pectoral 
lobe the scales are very much smaller. 
It is much to be regretted that the above-described fragment 
is all that has been saved of a specimen which was probably 
entire before the miner invaded its ironstone bed. Neverthe- 
less the discovery of the pectoral fin of Rhizodus is of great 
interest, inasmuch as it furnishes us with another most im- 
portant point of deviation of its structure from that of the 
Devonian genus Holoptychius, with which it was so long and 
sO obstinately confounded. In Holoptychius the pectoral, as 
shown by Prof. Huxley, is long and very acutely lobate, like 
that of Glyptolepis; the obtusely lobate corresponding fin of 
Rhizodus shows that it must be placed apart from these, in a 
distinct subdivision of the great Glyptodipterine family, along 
with its smaller congener Lhizodopsis. 
