8 



TJiomas Davidson — Spiral-Bearing Brac/iiopoda. 



important particulars with those obtained by Prof. Hall in N. 

 ventricosa. Nucleospira pisum is one of the most abundant species 

 in the Wenlock limestone and its underlying shales. 



Each spiral is found to consist, as I had previously stated, of not 

 more than six or seven convolutions, and the extremities of the spirals 

 are directed towards the lateral portions of the shell. The two 

 principal stems of the spiral coils are attached to the hinge-plate, 

 Fig. 6. and after extending a little way into 



the interior of the shell between the 

 spirals, are suddenly bent backwards 

 towards the hinge, and after forming 

 a curve converge, to about two-thirds 

 of their length, giving forth at that 

 place . short converging lamellce, 

 ■which unite in a sharp angular 

 point, the extremity being directed 

 towards the middle of the hinge- 

 plate. Each of the two primary 

 lamellfe diverge again as they pro- 

 ceed towards the front, and by a 

 gentle curve form the first spiral coil. 

 This arrangment is similar to that 

 described by Prof. Hall in his genus Menslina (20th Annual Eeport 

 of Eegents of the University of the State of New York, revised 

 edition, p. 186, 1868). In some specimens Mr. Glass has found 

 the V-shaped lamellee of which the inner branches are attached to 

 the hinge-plate extending downwards so as nearly to meet the 

 angular end of the connecting process, as is the case also in N. 

 ventricosa. In no instance, however (and a large number of speci- 

 mens have been operated upon), has Mr. Glass discovered any bifur- 

 cating process as in Meristella and Athjris. 



Genus EicTziA, King, 1850. 

 Nothing further relating to the type of the genus Eefzia, viz. 



Nucleospira pisum seen from the surface 

 facing the hottom of the dorsal 

 valve, from preparations by the 

 Eev. If. Glass. 



Fig. 7. 



Rctzia Salteri, developed Ly the Rev. 

 IS". Glass. 



Eetzia Adrieni, De Verneuil sp., is 

 known beyond the fact that the 

 shell was pi'ovided with spiral ap- 

 pendages. 



Prof. Hall devotes seven pages of 

 the Sixteenth Eeport of the Eegents 

 of the University of the State 

 of New York, 1863, to the genus 

 Jtdzia and to his genus Tremato- 

 spira. Eetzia ? Salteri and E. Bou- 

 chnrdi have been referred by Prof. 

 King, myself and other palaeonto- 

 logists to the genus Eetzia, and this 

 is where I should leave them, at 

 any rate until the internal appen- 

 dages of E. Adrieni shall have been 



