LaMELLIBRANCHIATA. | UPPER PALZOZOIC MOLLUSCA. 487 
AVICULOPECTEN INCRASSATUS (J/°Coy). 
Ref. and Syn. = Pecten incrassatus M°Coy, Syn. Carb, Foss. t. 16. f. 1. 
Dese.—Suborbicular, evenly convex, most so about the middle; apical angle about 110°; posterior ear 
obscurely defined, extending slightly beyond the edge of the shell, pointed, compressed; anterior ear much 
shorter, obliquely rounded, abruptly defined from the body of the shell, acute ; about twenty-five thick, rounded, 
radiating ribs, separated by slightly concave spaces rather wider than the ribs, on the body of the shell; ears 
nearly smooth or marked with lines of growth; surface with fine, irregular, obsolete, concentric wrinkles or 
strie of growth. Length ten lines, proportional width (from beak to opposite margin) ;4, length of posterior 
ear =, depth of left valve 2. 
This boldly marked shell is easily recognised by its numerous, strong, rounded, simple ribs, most of which 
are continued distinctly to the beak; the ears are sharply striated, parallel to the margin, but very indistinctly 
radiated ; the body of the shell has very delicate, short, discontinuous, membranous, concentric markings, which 
become larger towards the margin, where they give the ribs a slightly rugose character. The Pecten without 
a name, figured by M. de Verneuil (Geol. Russ. t. 21. f. 4.), from the pisolitic carboniferous rocks near Vitegra, 
seems to belong to this species. 
Position and Locality—Not uncommon in the carboniferous limestone of Derbyshire. The original Irish 
localities were, Calp, Bundoran, Donegal (rare) ; carboniferous slate, Lisnapaste, Ballintra. 
AVICULOPECTEN INTERSTITIALIS (Phill. Sp.) 
Ref. and Syn.= Pecten interstitialis Phill. Geol. York. t. 6. f. 24. (2+ Peeten intercostatus M°Coy, Syn. Carb. 
Foss. t. 18. f. 4.) 
Desc.—Obliquely ovate ; apical angle about 100°; surface with nine to eighteen narrow, sharp, radiating 
ribs ; between these are from three to nine smaller, the middle one of which is usually larger than the rest; all 
the ribs haye fine, compressed, hooked spines at close regular intervals, which, when broken, give them a tuber- 
cular aspect, and are separated by flat spaces about the width of the fine ridges ; ears with fine radiating ridges, 
and strong spines on the dorsal margin, both deeply defined from the body of the shell; anterior one nearly 
square, posterior one a little longer, pointed. Length eight lines, proportional width from the beak to opposite 
margin ;%, length of posterior ear ;;,, of anterior one nearly the same. 
This beautiful little shell appears to be very variable both in the number of the large ridges and the number 
of small ribs between every two large ones. It is very seldom that any of the delicate spines are preserved, 
the ribs more frequently presenting a roughened or tuberculated aspect, from their fractured bases. The 
great difference between the extremes of the varieties of this species induced me to separate them as above 
in my work on the fossils of the Irish mountain-limestone; I feel however, on examination of a still greater 
number of specimens, that it is necessary to reunite them, as the most, and least, simple forms of a singu- 
larly variable species. 
Position and Locality—In the black beds overlying the main limestone of Derbyshire. The original 
localities of the var. intercostatus were: lower limestone, Little Island, Cork, and abundant in the black upper 
limestone of Killymeal, Dungannon, so remarkable for the abundance and beauty of its reticulated corals. 
AVICULOPECTEN MACTATUS (de Kon. Sp.) 
Ref. and Syn. =P. mactatus de Kon. Anim, Foss, Bel. t. 5. f. 5. 
Dese.—Orbicular, slightly convex ; apical angle 105°; ears large, deeply defined by narrow steep slopes ; 
surface uniformly cancellated by nearly equal radiating and concentric elevated strize (three or four in the 
space of one line on all parts of the body of the shell); ears without radiating striz. Length one inch four 
lines, proportional width from beak to opposite margin ;3;, length of anterior ear ;;,, depth of right valve ;,. 
[rAsc. 111. | 3 R 
