Thomas Davidson — Spiral-Bearing BracMopoda. 5 



Monograph I figured the complete spiral appendages in Athyris 

 amhigua, Sow. My figures had been completed from several 



Fig. 3. 



Fig. 2 



Athyris planosulcata, developed by the Eev. N. Glass. 



specimens in the Museum of Practical Geology. Prof. Hall, in vol. 

 iv. p. 289, of his Paleeontology of New York, in 1867, described and 

 illustrated the spiral appendages of Athyris vittata, their mode of 

 attachment to the hinge-plate and the system of lamellce connecting 

 their two first coils. lu the main his description and figure would 

 agree with mine, but not quite so in details. In order that no mis- 

 conceptions should exist upon the matter, the Rev. N. Glass, at my 

 request, developed the spiral appendages and their connections in a 

 number of specimens of Athyris planosulcata and A. ambigua, which 

 had been liberally presented to him by Mr. John Tym, of Castleton. 

 As will be seen from the figures here appended, drawn from Mr. 

 Glass's worked specimens, his results would confirm the correctness 

 of my previous illustrations. 



In Athyris planosulcata Mr. Glass found that the first attachment 

 of each spiral takes place at the hinge-plate a. From thence the 

 two principal stems proceed for a short distance downwards, b, 

 when they suddenly bend backwards forming a broad rounded curve 

 facing the bottom of the dorsal valve b, d, e. At a little less than 

 half their length at d, each principal stem widens and gives off a 

 lamella d, h, which projects into the middle of the space interven- 

 ing between the two spiral coils, and here the lamellaj are connected 

 together and become exjoanded and roof-shaped. From the upper 

 portion of the expanded and roof-shaped pi-ojection h, a curved 

 lamella/ extends upwards and bifurcating at its extremity gives off 

 on either side a lamella g, which after forming a broad curve, and 



