630 BRITISH PALAZOZOIC FOSSILS. [ Pisces. 
This large ray is most allied to the G. tuberculatus (Ag.), from which it is distinguished by the much 
greater obliquity of the sculptured ridges, and the more compressed form of the section; the G. Alnvicensis 
(Ag.) has ridges nearly as oblique as the present species, but they are smooth and entire, instead of being 
strongly crenato-tuberculate. 
Position and Locality—vVery common in the dark shale (at the base of the carboniferous system), sup- 
posed to be of the age of the yellow sandstone in the valley of the Moyola, at Moyheeland, Draperstown, in 
the north of Ireland. 
Explanation of Figures—PI. 3. K. fig. 13, spine natural size, side view shewing part of the base of 
insertion, but broken at each end, from the yellow sandstone shale, Moyheeland, Draperstown ; fig. 13 a, ditto 
section, a little above the middle; fig. 14, ditto terminal portion, natural size, shewing the comparative smooth- 
ness of the ridges towards the apex, and the presence in that part of the posterior rows of denticles; fig. 14a, 
ditto portion of anterior face magnified. 
Genus. HELODUS (Ag.) 
Gen. Char.—Transvyersely elongate, crown convex, elevated along the middle into an obtuse conical 
ridge, sometimes divided into a line of several compressed cones diminishing from the centre ; surface porous 
as in Psammodus ; margin of the crown raised in the middle on both the inner and outer sides, and it and the 
root vertically plicated. 
This is manifestly but a subgenus of Psammodus, from which it is only separated by the gibbosity of the 
crown. 
HELopus pipymus (Ag. name only). PI. 3. I. fig. 18, 19, 20. 
Dese.—Crown of tooth usually much elevated in the middle into a very prominent cone, more or less 
deeply notched at the apex, and haying from that notch a more or less distinct sulcus extending towards the 
base of the crown, the border of which is elevated in the middle, particularly the posterior side close to, or 
vertically over which, the double apices of the cone usually incline. Surface, coarsely granulo-punctate, most 
so on the end of the middle cone, leaving the ends of the tooth nearly smooth (the granules being closed and 
elevated in the unworn tooth, but impressed puncta in old ones). Width of average, or rather small specimen, 
four lines, height two a half lines, but sometimes more, and often less. 
The notching of the apex of the submedian cone, and the still more rarely seen sulcus therefrom, con- 
stitute the only differences between this species, and the more elevated varieties of H. turgidus, to which I have 
no doubt it should be referred as a variety. 
Position and Locality —Rare in the lower carboniferous limestone of Armagh. 
Explanation of Figures —P\. 3.1. fig. 18, obscurely notched, punctured specimen; natural size; fig. 
18a, profile of ditto, shewing the posterior margin at a much higher level than the interior one; fig. 19, 
deeply cleft specimen, front view; fig. 20, very narrow pointed specimen, back view; 20a, ditto, front view. 
HELopus La&vissimus (4g.) Pl. 3.1. fig. 17. 
Ref.—Ag. Poiss. Foss. Vol. III. t. 14. fig. 1 to 15. 
Desc.—Tooth polymorphous, some specimens having the form described for, Ist, H. twrgidus ; 2nd, that of 
H. mammillaris ; 3rd, others are transversely oval, and moderately convex ; the surface of all is usually smooth, 
and highly polished, but this character is only partial; and I have no doubt that the gibbous specimens should 
be referred to the H. twrgidus, in which, as I have observed in the Psammodonts generally, a lustrous, thin 
layer of ganoine, in certain states of the surface, conceals the punctation; the forms like mammillaris might 
be referred to that species. The remaining transversely oval, moderately convex specimens, which cannot 
be referred to any other species, are sometimes as strongly punctured as the H. planus. 
