LIMATULINA DESQUAMATA. 37 



Limatulina alternata, M'Coy, sp., 1844. Plate XIX, figs. 7—10, 12. 



Lima alternata, M'Coy, 1844-. Syuops. Carb. Foss. Ireland, p. 87, pi. xv, fig. 4. 

 — peisca, M'Coy, 1844. Ibid., p. 88, pi. xviii, fi^. 6. 



Specific Characters. — Shell small, narrow, produced downwards, very gibbose, 

 righl valve less so than the left, slightly oblique. The anterior border long, gently 

 convex, the lower margin more round, and the posterior elongate and almost 

 straight. The hinge-line short and straight. The umbones small, pointed, 

 central, that of the left valve overlapping the right valve. Ears not defined. 

 The anterior ear of the left valve rolled, the posterior gently and gradually com- 

 pressed. An elongate area along the hinge-line. 



Interior. — -Unknown. 



Exterior. — The surface is ornamented with numerous fine, somewhat sinuous, 

 fibrillose, radiating ribs, often alternately large and small. The ribs are often 

 moniliform, being broken up below into rows of irregularly sized tubercles. Both 

 valves have a similar ornament. Concentric lines and rugae of growth, irregular 

 in strength, cross the ribs at various intervals. 



Dimensions. — PI. XIX, fig. 8, a specimen from Narrowdale, measures — 

 Antero-posteriorly . . . .29 mm. 



Dorso-ventrally . . . .24 mm. 



Localities. — England : the Carboniferous Limestone of Hill Bolton, Yorkshire; 

 Narrowdale, Staffordshire; Park Hill, Derbyshire; Poolvash, Isle of Man. 

 Ireland: Blackrock and Little Island, and Streamhill, co. Cork; Ardagh, co. Meath. 



Observations.— 1 have examined the types of M'Coy's species Lima alternata 

 and L. prisca, and have come to the conclusion that the latter is only the young 

 and therefore less expanded form of the former. Whether or no the valve shows 

 alternating ribs, depends entirely on age. I have been fortunate enough to obtain 

 specimens of both valves, and the right is certainly flatter than the left valve. 

 L. alternata is easily distinguished from all other species of the genus by its 

 peculiar and highly ornamental markings. The shell seems to have been very thin 

 in full-grown examples, as it is often found expanded and buckled. 



Streblopteria ellipsoidea and Limatulina Ungaata, de Koninck, have an appear- 

 ance and contour very similar to M'Coy's shell. 



Limatulina desqtjamata, M'Coy, sp., 1844. Plate XIX, figs. 11, 20—23. 



Pteeinea desqttamata, M'Coy, L844. Sjnops. Carb. Fuss. Ireland, p. 82, pi. xiii, 



fig. 2. 

 Pecten conoibeub, M'Coy, 1814. Ibid., p. 91, pi. xvii, fig. 2. 



