CARBONIFEROUS FOSSILS OF IRELAND. 165 



Bairdia gracilis. M'Coy. (PL XXIII. fig. 7)- 



Sp. Ch. — Length three and a half times the depth ; dorsal and abdominal margins parallel. 



The diameter is about two-thirds the depth; the abdominal margin is convex at both ends, and concave 

 in the middle ; the dorsal margin is concave at both ends, and convex in the middle, they are consequently 

 nearly parallel ; both ends are alike. Length half a line. 



Cythere amygdalina. M'Coy. (PL XXIIL fig. 8). 



Sp. Ch. — Length rather more than twice the depth ; one end small, rounded, submucronate ; the other 

 much larger, obtusely rounded ; valves convex ; surface smooth. 



This species has mucli the shape of the C. excavata, M'Coy, but is more slender, has more unequal ends, 

 and is entirely without marks or impressions of any kind. Length half a line. Common. 



Cythere arcuata. M'Coy. (PL XXIIL fig. 9.) 

 Sp. Ch. — Slender, rounded, twice as long as deep, arcuate, convex, the dorsal margin very convex, ventral 



margin nearly equally concave ; surface smooth, without markings. 



This little species is very common in the carboniferous shales, and although rarely well preserved, is easily 



recognized by its lengthened, curved form ; it differs from Bairdia //racilis, jM'Coy, and the allied species, by its 



simple, obtusely rounded extremities. Length about half a line. 



Cythere bitubercdlata. 31' Coy. (PL XXIIL fig. 10). 



Sp. Ch . — Twice and a half longer than deep ; ventral edge long, straight ; back but slightly convex ; both 

 ends nearly equally rounded ; sides flattened ; each valve with two very large, rounded tubercles, situated rather 

 more than their own diameter, one from the anterior, the other from the posterior end. 



This very distinct and beautiful species is common in one or two localities ; it is easily known from the 

 other species I have described, by the two large tubercles on each valve. Length one-third of a Hne. 



Cythere cosTATA. M'Coy. (PL XXIIL fig. 11). 



Sp. Ch. — Ovate, rounded, gibbous ; abdominal margin very convex ; ends obtusely rounded ; the anterior 

 shghtly narrower ; a deep circular depression in the centre of each valve, and each side ornamented with four, 

 longitudinal, slender ridges, and one following the curve of the abdominal margin and ends ; three or four 

 obtuse, rounded tubercles at the anterior end. 



I have seen several specimens of this very distinct and beautiful species, which is, however, one of the 

 rarest and most solitary of the genus. It is easily distinguished from all others by its beautifully costated sides ; 

 the number of tubercles at the anterior end is also remarkable. Length half a line. 



Cythere CORNUTA. M'Coy. (PL XXIIL fig. 12). 



Sp. Ch. — Shell sub-rhomboidal, gibbous; an obtuse spine near the centre of the abdominal margin of each 

 valve. 



This is distinguished at a glance from the C. spinigera, M'Coy, by having the spiniform tubercle in the 

 middle or nearly so, of the abdominal margin ; the posterior end is obtusely rounded, while the anterior 

 end gives a slight obliquity to the contour of the shell ; the dorsal outHne is gradually curved, the abdominal 

 somewhat undulated, but without a sinus. This shell is most inflated at the back, and gradually diminishes in 

 diameter towards the abdominal edge; the sides are not, however, concave, one valve overlaps the other 



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