BRITISH SILURIAN BRACHIOPODA. 83 



Nucleospira, I feel disposed to class it provisionally with the Nudeospiridcs. There is 

 this important difference, namely, that the principal stems, instead of running parallel to 

 each other, are widely separate, and, after extending parallel to each other for a short 

 distance, bend at right angles abruptly towards the lateral portions of the beak, and form 

 two large curves facing the lateral portions of the valve. The extremities of the spiral 

 coils are, however, directed towards the lateral portions of the shell. 



Un CITES we place here also provisionally, although it differs from Nudeospira in 

 several particulars, and especially in its simple mode of attachment to the hinge-plate. 

 The principal stems of the spiral coils are, however, connected in a similar manner to those 

 of Nudeospira, and the extremities of the spiral cones are directed towards the lateral 

 margins of the shell (see * Devonian Supplement ' for full details and illustrations). 



3. Family — Athyrid^, Phillips, 1841. 



This great and important group of spiral-bearing Brachiopoda comprises — 



fAthyris, M'Coy, 1844; types A. concentrica^ von Buch. ; and ^. 



plano-sulcata, Phillips (= Spirigera, d'Orbigny). 



First Division \ Kayseria, Dav., 1882; type K. lens, Phillips. 



I Whitfieldia, Dav., I88I ; type W. tumida, Dalman. 



(^Bifida, Bav., 1882; type B. lepida, Goldf. 



- ^. . . ( Merista, Suess., 1851 ; type M. herculea, Bar. 

 Second Division ■< ,^ . , ,, r^ 77 ^o^,^ . 1,^ , tt ,i 



C Meristella, Hall, 1860 ; type M. arcuata. Hall. 



All these genera are fully described and illustrated in the ' Devonian and Silurian 



Supplements.' The extremities of their spirals are directed towards the lateral portions 



of the valves. Their primary lamellae are generally attached to the hinge-plate in a 



similar manner, although differing somewhat in detail. The primary stems of the spirals 



are connected in a variable and more or less complicated manner by a system of lamellae 



termed " the loop." In the first division the loop is forked and the accessory lamella 



more or less extended ; in the second division the loop forms two rings. 



4. Family — ATRYPiDiE, Ball, 1877. 



This extensive family may include all those genera which have the apex of their 

 vertical spiral cones directed towards the bottom of the dorsal valve, and might be 

 provisionally divided into three separate groups.^ 



1 Dall, in his index to the names which have been applied to the subdivisions of the class Brachiopoda 

 previous to the year J 877, includes in his family ATRYPiUiE Atrypa, Anoplotheca, Zygospira, Ccelospira, 



