E, Billings on Prof, HalVs recent puhlication, 393 



osaurus, it could not be retained, no matter how long in use, 

 because it would be absurd to give a Trilobite a name which would 

 imply that it is a Crinoid or a Saurian. So with Cyprkardites, 

 The name implies a close aflSnity with Cypricardia, sl genus of the 

 family OrpRiNiDiE, while the fossils to which Prof. Hall would 

 apply it belong to a different family, Arcade, or rather to a 

 group which appears to form a passage between that family and 

 AvicuLiD^. The name Athyris, quoted by Prof. Hall as afford- 

 ing an analogous case, is quite a different instance. It does not 

 refer the genus to any family, and is only objectionable when used 

 for species with a perforated beak. And for this reason, some of 

 the best palaeontologists reject it altogether. Even Mr. Davidson 

 who still uses it, says that he would have adopted D'Orbigny's 

 generic name Spirigera^ had he not been influenced by other au- 

 thors (British Carboniferous Brachiopoda, p. 79). The greatest 

 authority on the Brachiopoda thus retains Athyris for shells with 

 perforated beaks, simply in deference to the views of others and 

 contrary to his own convictions. 



5. The genus Zygospira^ p. 126, is not separable from Atrypa, 

 The connection of the two spires is not of generic importance. 

 The same structure occurs in Spirifera^ some species of which 

 have the spires connected and others not. Atrypa modesta is 

 scarcely distinguishable from A. erratica [Orthis erratica of the 

 Pal. N. Y., Vol. 1), and this latter again passes into A. Headi, 

 In these two species the shell structure is precisely that of A, 

 reticularis. I have referred them to Athyris^ at the same time 

 stating that it would become necesssary to place them in the genus 

 Atrypa^ should the position of the spires be found similar to those 

 of that genus. (See New Species of Lower Silurian Fossils, June 

 1862, p. 146.) 



6. Orthis emacerata^ PI. 2, figs. 1, 2, 3, is not separable from 

 0. testudinaria. 



Y. The mistakes with respect to Barrandia and Clioderma 

 were first pointed out by me, and so were the affinities between 

 Rhodocrinus and Thysanocrinus. The corrections are published 

 in this book as if they were original. 



8. Specimens of Phragmostoma from Tennessee in my posses- 

 sion have a circular aperture in the septum. 



