SPIRIFERA. 



45 



occupied by the spiral cones, which were fixed in the usual manner to the projections of 

 the inner socket walls of the dorsal valve. Two examples measured — 

 Length 2 inches, width 4 inches, depth 3 inches. 

 Length 2 inches 9 lines, width 2 inches 10 lines, depth 2 inches 5 lines. 

 Obs. The external characters of Sp. cuspidata were correctly described and illustrated 

 by Martin as early as 1796, and but little has been added concerning its internal arrange- 

 ments. Having, through the kindness of Mr. Kelly, obtained a certain number of Irish 

 specimens, I fractured a few in order to ascertain more correctly the true position and 

 dimensions of the dental or rostral shelly plates, which have already been described, and 

 which will be found illustrated in the accompanying cut. 

 It is quite evident that the shell under description be- 

 longs to the genus Spirifer proper, and not to the sub- 

 genus Cyrtia, as supposed by Professor M'Coy, and in 

 which opinion I had coincided before having become 

 fully aware of its complete internal arrangements. No 

 specimen of Sp. cuspidata I have hitherto been able to 

 examine has exhibited the deltidium in its entire con- 

 dition, but which, in all probability, was not perforated 

 by a circular foramen, as is seen in true types of the sub- 

 genus Cyrtia, such as in C. trapezoidalis and C. Murchi- 

 soniana. Nor do I perceive upon what grounds Professor 

 M'Coy asserts that the fissure displays a deep-seated 

 pseudo-deltidium. 



The position of the dental plates is defined on the exterior of the shell by two diverg- 

 ing lines (PI. VIII, fig. 22 s) departing from the extremity of the beak, and are more 

 clearly visible in those examples (by far the more numerous) wherein the shell is but 

 imperfectly preserved. It was to compressed shells from the lower limestone of Black 

 Rock (Cork), on which the ribs were almost obliterated, that Professor M'Coy identified 

 the Devonian Sp. simplex of Phillips, a mistake which Mr. Salter and myself were able to 

 correct from the inspection of the original examples so named, and kindly communicated 

 by Dr. Griffith. Other species have also been inaccurately referred to Martin's shell ; 

 these will be found enumerated in Professor De Koninck's work on Belgian fossils. 



Some varieties of Sp. cuspidata (fig. 20) have been referred to the Devonian Sp. 

 macroptera of Hall, in which the area is narrower and less developed than is usually the 

 case in typical examples of Martin's shell. These varieties occur plentifully in limestone 

 and millstone grit, near Kendal, but at the same time present every intermediate link 

 connecting those individuals with a narrow area to the typical form of the species under 

 description. This fact was pointed out by Professor M'Coy, at p. 426 of his work on 

 'British Palaeozoic Fossils,' but I do not perceive that there exists any proportional dif- 

 ference in the width of the fissure as described by the Professor, and many of the examples 



Spirifera cuspidata. 



X. Area. S. Dental or rostral plates. 

 L. Coil of the spirals. 



