110 



SUPPLEMENT TO THE 



Atriipa reticularis, from tlie Lower Hil 

 derberg- gjroup of Albany County, New 



and shape of the spiral appendages, at first attached to the hinge-plate of the dorsal valve, 



and placed side by side, with their extremities facing 

 the middle of the bottom of the dorsal valve, may be 

 seen in the accompanying figure. 



Mr. Glass has also developed the complete interior 

 of A. reticularis from English si)ecimens, and they show 

 all the characters so well described and illustrated, in 

 1866, by Professor J. Hall and Mr. R. P. Whitfield. 

 The principal stems of the spiral coils, at a short dis- 

 tance from their attachment to the hinge-plate, are 

 connected by a narrow band, the branches from either 

 side converging downwards into a V shape, and each 

 branch slightly turned up at its extremity. This 

 iTrt^fre"CVro?S\^HriXTiu.wfngre ^'''^"^^ ^^^^^ coutinuous in manv specimens that have 

 tWo/sa?vai've'' ""'^ "P''"*=^ ^^ ''""''^^'^ *° bccn Operated upon ; but, as stated by Mr. W. Gurley/ 



in some individuals this loop or band would appear to 

 be disunited, the inner ends opposing each other without being actually connected. 

 This act is also corroborated by Professor Quenstedt, who, in the Atlas of his 

 ' Brachiopoden,' pi. xlii, fig. 87 «, draws the disunited band as described and figured 

 by Gurley. Through the kindness of Professor James Hall I have been able to 

 examine two perfect specimens from the Lower Helderberg group near Clarkesville, 

 Albany County, in which the crural processes or loop seem so 

 close as almost to come in contact at their turned-up extremities, 

 but I question whether they formed always a continuous unin- 

 teirupted band. Again, in another specimen, Atrypa spinosa. 

 Hall, from the Hamilton group, Darien, New York, the crural 

 processes seem to form an uninterrupted band, as is the case 



Atrypa reticularis, from 

 Lower Helderberg group, near 

 Clarkesville, United States. n • -ii i • i i i • r t) v i. 



a. Disunited extremities of blcewisc witli somc adnnraoly prepared specimens oi liritisn 



the loop or crural processes : 

 b, first coil of tile spire; c. 



A. reticularis worked out by the Rev. Norman Glass, and of 

 hi'n?e-pfate"'"''™'°* *° *^'' ^^^^^ ^6 have givcu figurcs in two of the plates of the ' Silurian 



Supplement.' 

 Having, thanks to the liberality of Mr. G. ]\Iaw, been able to examine several 

 thousand specimens of ^. reticularis, I have ascertained how much it varies in shape, and 

 especially at different stages of growth. The smallest or youngest examples measured 

 not much more than half a line in length and breadth, and every stage was obtained up 

 to shells measuring one inch and a half in length and breadth. When quite young the 

 dorsal valve is nearly flat, with a strongly-marked longitudinal mesial depression ; this 



' ' Proceedings of the American Philosophical Society,' vol. xvii, p. 337, pi. xiv, 1878. lu 1873 

 Mr. Salter, at p. 55 of a ' Catalogue of the Collection of Cambrian and Silurian Fossils in the Woodwardian 

 Museum,' gave a good figure of the interior of Atrypa reticularis, showing the crural processes united. 



