LBIOPTERIA LAMINOSA. 15 



behind, marked off posteriorly from the Aviug by an almost obsolete linear oblique 

 depression. The postero-inferior part of the valve is broad and expanded. The 

 posterior wing is triang-nlar, with a falciform margin, compressed and expanded, 

 and seems to extend further l^ack tlian the postero-inferior angle. Byssal sulcus 

 well marked. 



J lifer lor. — There is an excavated circular pit for the anterior adductor muscle. 

 The pallial line is entire. 



Exterior. — The surface is ornamented with concentric laminose lines and striae 

 of growth of irregular character. At times this condition is so nnich accentuated 

 as to become subimbricating. 



Dimensiom. — PI. Ill, fig. 6, tlie original of Phillips's species, measures — 

 Antero-posteriorly .... ;]8 mm. 



Dorso-ventrally . . . .32 mm. 



From side to side (estimated) . . .16 mm. 



Locolities. — England : the Carboniferous Limestone of Hill Bolton, Withgill, 

 Scalber, and Settle, Yorkshire; Castleton, Thorpe Cloud, Park Hill, Derljyshire; 

 Poolvash, Isle of Man. Scotland : Corrieburn, Kilsyth. Ireland : Clane, co. Kildarc. 



Observations. — The type specimen, PI. Ill, fig. G, is preserved in the Gilbertson 

 Collection, Natural History Museum. It is a left valve, not quite perfect in front 

 or at the posterior inferior part. As far as I am able to judge, this specimen 

 represents the fully grown individual. Much less transverse and triangular than 

 //. Thomjysotii, the absence of any distinct lunate ridge, and the more <|uadrate form, 

 distinguish the species from L. himilata. 



The size and extent of the posterior wing is to be noted. Unfortunately, 

 owing to the extension and thinness of the anterior and posterior extremities, one 

 or other is frequently missing. The type, PI. Ill, fig. 6, shows a perfect posterior 

 wing; PI. Ill, fig. 7, a perfect anterior end. It is probable that several of de 

 Koninck's species represent imperfect or immature forms of L. laminosa. L. 

 Phillipsii, L. gihhosa, L. rostrata, L. strangulata, L. intern ledia, and L. uinjnla seem 

 to me to have much in common with the species. I think that there is good evidence 

 that the shell was more quadrate in the younger stages of growth than when full 

 o-rown — a fact which will account for some of the supposed species. In some of 

 my specimens the rostrum seems to have been broken off or rubbed down during 

 life. Casts of the interior would not sIioav the peculiar shape of the posterior end, 

 owing to the approximation of the opposing posterior wings ; hence another soui-ce 

 of error in determination of species. In incomplete specimens it is advisable to 

 determine the shape of the shell by tracing the contour shown by one of the lines 

 of growth, and allowing for the extension of the rostrum. 



