88 
PALEONTOLOGY OF NEW YORK. 
growth, developed earlier in some species than in others, and hence the term 
was essentially a misnomer. On this account some authors, particularly the 
French and German writers, have preferred to use the term Spirigera, pro¬ 
posed by d’Orbigny in 1847* * * § to replace Atiiyris, and founded on the same 
species. The term Euthyris, also, was proposed by the late Professor Quen- 
STEDT,f but it has not come into general use. Among generic appellations 
there are too many misnomers which have an established and positive value, 
to permit the rejection of the term Athyris without great inconvenience, 
attended by no equivalent advantage. The term is therefore used in a re¬ 
stricted application and substantial reasons will be given for a subdivision of 
the gen us. j; 
The essential feature which forms the basis of union of all the variations of 
the genus here discussed, is the nature of the loop. This complicated struc¬ 
ture was first demonstrated by Davidson in 1857 § for the species Athyris 
pectinifera, Sowerby. Since that date our knowledge of this organ has become 
more extended and more exact, and we now know its peculiarities in several 
species from the Devonian, Carboniferous and Permian faunas. 
Athyris concentrica, representing a combination of characters which expresses 
the typical phase of athyroid structure, is distinguished from the subordinate 
divisions of the genus by the following differences; 
(a) The usually transverse form; this is a feature subject to variation, but 
throughout the group this outline is striking, simply from the frequency 
of its occurrence. 
{b) The lamellar expansions or varices at the concentric growth-lines are 
simple, that is, are not split up into spinules, nor do they embrace 
such spinules, but are usually transversely striated. They are often 
highly developed toward the margins of the valves, but are generally 
* Comptes rendiis, vol. xxv, p. 268. 
t Petrefactenkunde Deutschlands, p. 442. 1871. 
I Students who may wish to follow the variation of opinion in regard to the value of the genus Athteis, 
are referi-ed to a paper by the late Mr. Bilungs, Palaeontologist of the Geological Survey of Canada, “ On 
the Classification of the Subdivisions of McCoy’s Genus Athyris, as determined by^ the Laws of Zoological 
Nomenclature American .Tournal of Science, vol. xliv (1867), p. 48. See, also, vol. Nxxiii of the same 
Journal, pp. 127, et seq. 
§ British Permian Brachiopoda, p. 21. 
