124 SUPPLEMENT TO THE 



and curving gently passes over the apices of the spires. In the other the origin of the 

 loop appears to be at a higher point, or otherwise it lies parallel with the outer curve of the 

 spiral for some distance, and stretches from one side to the other between the spires and 

 the base of the crura. This difference may be accidental, or may be caused by displace- 

 ment of the loop in the one case; in both, however, the essential features are preserved.'* 

 In page 3G7, 1868, of the 'Twentieth Annual Report,' Prof. Hall reproduces his 

 description and figures, adding : " At that time the spires of Atrypa were not known to 

 be connected by a loop, as has since been ascertained ; and this renders the analogy 

 between the genera still more close. In Zi/gospira the spirals are more obliquely directed 

 towards the centre of the dorsal valve than in Atrypa ; the loop is attached much lower 

 down on the limb of the spire, and is more direct, as is shown in the accompanying 

 figure of Atrypa reticularis, and the spiral coils are much more lax. These features 

 might not be of generic importance." 



Feeling very uncertain, as Prof. Hall himself appears to have been, as to which of 

 his figures was the correct one, I asked Dr. G. J. Hinde to kindly send to me and 

 to the Rev. N. Glass some specimens of Zygospira modesta he had collected from several 

 Canadian localities, that Mr. Glass might examine their spiral characters so as to 

 determine without doubt which of Prof. Hall's figures was the correct one. 



Dr. Hinde, with his usual liberality, placed in the hands of Mr. Glass a large 

 number of the specimens of Zyyospira modesta peculiarly favorable to Mr, Glass's 



operations, being filled with spar, and Mr. Glass was 

 thus enabled to develop the spirals, loop, and attach- 

 ments to the hinge-plate in six specimens, and found 

 that they all agreed, and that in none of them was 

 the loop placed so low down as in Prof. Hall's fig. 1, 

 T j^ \ f\\ W V^) ^'J jj ] '^ I "1 ^li^c^ figure we have reproduced at page 111 of this 

 ir!^ \\ V\ N^ ^^^JJ }j / Supplement. His fig. 2 is, in the main, the more 



correct representation.^ 



In the description of the species recurvirostra, 

 given a few pages further on, it will be seen that the 

 T^Tt::;:'S:^^^^^^ loop in that species bears some resemblance to the 

 tX^^t:^^rS^. '^''-'^'- supposed loop of Z modesta in Prof. Hall's fig. 1. It 



might therefore have been imagined that Prof. Hall had 

 seen some preparations of recurvirostra, and had based his fig. 1 upon it ; but this could 

 hardly have been the case; first, because the shell, as given in fig. 1, is the same as in 

 fig. 2 ; and, secondly, because the loop in Prof. Hall's fig. 1, taken in connection with the 

 primary lamellae on each side of it, is wide and extended, and not oval and compressed, 

 as is the case in recurvirostra. So far as Z. modesta is concerned, Hall's fig. 2 must be 



1 Since the above was in type Mr. Whitfield has sent me a prepared specimen agreeing in every 

 particular with those cleared out by the Rev. Norman Glass. 



