Mr. E. Billings on the Genus Atbyris. 235 



of knowledge of all palaeontologists conversant with the fossils 

 of the older rocks, and might be thought superfluous. But the 

 question is somewhat complicated, and cannot well be decided 

 unless in view of all the circumstances. Besides this, it is one 

 upon which any good naturalist is perfectly competent to give 

 an opinion although specially engaged in other departments. 

 Few of these have access to works on palaeozoic fossils; and 

 therefore, for the convenience of such as may feel inclined to 

 investigate the subject, it is desirable to bring all the facts to- 

 gether. 



There is no dispute about the extent of the genei'a; and there- 

 fore the details of the internal characters need not be given. It 

 is purely a question of natural-history ethics, if I may be per- 

 mitted to use such a term. 



1. History and Extent of the original Genus. 



The original description was published in the ' Synopsis of 

 the Carboniferous Fossils of Ireland,^ in 1844. From this work 

 I shall make some extracts, and shall introduce along with the 

 original figure two others to further illustrate the subject. 



Fig. 1. Copy of the original figure given by M'Coy (without a specific 

 name) to ilhistrate his idea of the general form of an Athyris. 



Fig. 2. Spirigera concentrica, Von Buch. The form is copied from 

 Davidson's Monograph of the British Devonian Brachiopoda, 

 pi. 3. fig. 13, Pal. Soc. Mon. for 1862. The right-hand side is, 

 in this copy, a httle restored, and the aperture in the beak made 

 larger than it is in the original figure. 



Fig. 3. Athyris tumida, Dalman. Copied from Davidson's ' General In- 

 troduction,' pi. 6. fig. 73. 



The following extracts are from ^I'Coy's work above referred 

 to:— 



" The family Delthyridse appears to be divided into the five fol- 

 lowing genera : — 1 . Spirifera, Sow., composed of those longitudinally 

 ribbed species in which the hinge-line is equal to, or exceeds, the 

 width of the shell, the cardinal area with parallel sides, the cardinal 

 teeth of the ventral valve [now called the dorsal valve] large, spirally 

 rolled, and having a triangular foramen beneath the beak of the 



16^ 



