264 
Proceedings of the Royal Society 
high in front, with concavely cut out posterior margin ; the height 
of the dorsal in front is 1 J inch, its base of origin is disturbed ; the 
apex of the anal is imperfect, its base measures inch. Their 
rays are numerous, slender, and smooth, dichotomising only near 
their extremities, and having their transverse articulations compa- 
ratively distant. The caudal, as it lies before us, can hardly be 
called inequilobate, but as the upper lobe appears somewhat 
crumpled, its entire length is probably not accurately exhibited. 
It is deeply bifurcated, the lower lobe being narrow and of great 
length, measuring 1 J inch, though its extreme point is cut off ; its 
rays are like those of the dorsal and anal, being slender, smooth, 
and with rather distant articulations, the joints being at first more 
than twice as broad, but getting a little closer towards the end of 
the rays ; in the upper lobe the rays are, as usual, short and very 
delicate. Small and closely set fulcra are observable on the ante- 
rior margin of all the fins. 
Remarks. — It is of course at once evident that the present species 
is closely allied to the powerful Nematopty chins Greenockii , A g. sp., 
of the Wardie Shales; it differs, however, from the latter in several 
particulars beside its smaller size. The transverse articulations of 
all the fin-rays are considerably more distant ; and the principal 
rays of the pectoral are unarticulated for a greater distance than is 
the case in N. Greenockii. The form of the laniary teeth differs 
also somewhat in the two species. In N. gracilis these are more 
regularly conical, gradually tapering from the base to the apex; 
whereas in N. Greenockii they assume a more slender form, owing 
to the more sudden narrowing of the base upwards into the body 
of the tooth, although the relative proportion of the diameter of 
the base to the length of the tooth is about the same. The specific 
name “ gracilis ” is bestowed on the present species in allusion to 
the slender and elegant shape of the body. 
Geological Position and Locality. — The two specimens above de- 
scribed were found in the blackband ironstone at present wrought 
in Yenturefair Colliery, Gilmerton, near Edinburgh, and are both 
preserved in the Museum of Science and Art, Edinburgh. This 
ironstone, well known for its Rhizodus remains, is a member of the 
Lower Limestone group of the Carboniferous Limestone series of 
the Lothians, and occurs along with the North Greens coal-seam, 
