THE LAMELLIBRANCHS OF THE SILURIAN ROCKS OF GIRVAN. 539 



Interior. — The hinge plate has a strong oblique tooth in the left valve, with a 

 corresponding pit in the right valve. No lateral teeth. Anterior adductor scar deep 

 and rounded, almost marginal. The posterior less well marked. A strong process 

 posterior to the anterior adductor scar, leaving an elongate slit in casts, as in 

 Clidophorus. Pallial line entire. 



Exterior. — Surface ornamented with fine concentric lines of growth. 



Observations. — Phillips, discussing the relationship of some palaeozoic shells to the 

 Mytilidae, speaking of Cypricardia cymbseformis, says : " If, as I suppose, C. 

 cymbeeformis be distinct generically and include species of the Mountain Limestone, 

 the name Go?iiophora seems suitable. It is, however, doubtless a mytiloid shell." 

 Hall adopted Phillips' proposal, and the type is to be regarded as C. cymbseformis. 

 I was unable to find a single tooth in the Carboniferous forms, and invented the genus 

 Mytilomorpha to receive them, Brit. Carb. Lamell., p. 338, where I have discussed 

 the systematic position of Goniophora at length. M'Coy refers Cypricardia 

 cymbseformis to Orihonotus. Conrad does not seem to have noticed Phillips' 

 proposal to place it as the type of a new genus. 



Goniophora antiqua, sp. nov. (PL IV., figs. 24-27.) 



Specific Characters. — Shell transverse, strongly carinate, oblique. Postero-inferior 

 angle produced and pointed. Anterior end small, its margin rounded. Inferior border 

 slightly convex. Posterior border oblique, straight, making angles with the upper and 

 lower margin. Hinge line straight, short, and erect posteriorly. Umbones, anterior 

 almost terminal, incurved, and somewhat prosogyrous, contiguous. Proceeding from 

 the umbo to the postero-inferior angle is a strong angular ridge along which the shell 

 is bent on itself so that the posterior slope is placed at an angle with the rest of the 

 valve. In front and below the ridge is two-thirds of the shell, which is very gently 

 convex, and shows only slight indication of any constriction. The dorsal slope is 

 rapidly compressed and flattened. There appears to be an escutcheon, marked off by 

 a shallow curved line on each side of the raised hinge. 



Interior. — Hinge not seen. Muscle scars normal. 



Exterior. — The lower and anterior part of the valve is almost smooth, but the 

 triangular depressed dorsal slope is covered by regular, equidistant, close, raised lines, 

 parallel to the posterior margin. 



Dimensions. — Fig. 24, PI. IV., measures: antero-posteriorly, 18 mm.; dorso- 

 ventrally, 7 mm. ; from side to side, 9 mm. 



Locality. — Scotland : Llandeilo beds, Ardmillan ; Penkhill, Upper Llandovery ; 

 Woodland Point, Middle Llandovery. 



Observations. — There are four specimens of this species in the Gray Collection. It 

 differs from G. carinata, Hall, sp., from the Trenton Limestone, in possessing a much 

 less produced anterior end, and has an obsolete byssal sinus. 



