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Proceedings of Royal Society of Edinburgh. [sess. 
of subjacent vascular channels. Associated with these scales is a 
small tooth, shaped as in Strepsodus sauroides, hut with the striation 
of a much more delicate character (Museum of Science and Art). 
Megalichthys Icevis, n. sp. — I apply this term to a comparatively 
small species of Megalichthys , whose more or less disjointed remains 
are not uncommon in the ironstone nodules contained in the “roof ” 
of the Dunnet oil shale worked at Straiton and Pentland. Its dis- 
tinguishing specific character is the thinness of the scales and the 
absence of the usual prominent rib or keel on the under surface. 
In fact, these scales, when seen from below, are almost indistinguish- 
able from those of Rhizodopsis. Externally they are brilliantly 
ganoid on the free portion of the surface, as in other species. Type 
specimens in the Museum of Science and Art, Edinburgh. 
Elonichthys nemopterus, Ag. — After puzzling for years over in- 
numerable specimens of the Robisoni type of Elonichthys , which is 
so common in the Lower Carhoniferous Eocks of central Scotland, 
and in vain seeking for definite characters towards dividing them 
into “ good ” species, I have been reluctantly compelled to abandon 
the quest, and to seek for a solution of the question by reuniting 
them all, with the exception of E. Buchlandi (Ag.), which can always 
be easily recognised by the strongly-marked and deeply-cut orna- 
ment of its scales. 
It is no doubt easy enough to put together a set of extreme forms, 
which any one might readily be tempted to adopt as distinct species, 
and in fact I did so myself at the commencement of my investiga- 
tions ; but the more material I obtained, the more and more unre- 
liable did I find every character turn out upon which I had fixed 
as diagnostic. Eor example, the relative fineness or coarseness of the 
fin-rays, and the relative distance of their transverse articulations, 
are characters which are quite inconstant. As a rule, the fin-rays 
are proportionally more slender and more distantly articulated in 
young specimens, though this condition sometimes persists in adult 
forms. Also, no reliance can be placed on the relative extent to 
which the scales are striated or punctate, or upon whether the 
punctate area is nearly smooth or thickly covered with punctures. 
Unfortunately the relative size of the scales and the number of rays 
in each fin are characters which can only be accurately ascertained 
in exceptionally well-preserved specimens, as a certain amount of 
