PALASTBRINA PRIMXVA. 223 



The madreporite is a large thin plate. It presents features which I do not 

 understand. Text-fig. 150 has an appearance which suggests that it is embedded 

 in a membrane overlying the interradial plates. Its inner proximal surface over- 

 rides the adambulacralia in an obviously unnatural position. The whole appearance 

 indicates that the madreporite overlaid a large vesicle which projected oralwards 

 and collapsed after death. The thin madreporite was forced down on to the adam- 

 bulacralia and became slightly fractured during this process. 



Ad. 



Text-fig. 160. — Wash-drawing of the floor and inner wall of the ambulacral groove of Palasterina primxva 

 (from Sedgwick Mns.). Ad., adambulacral ; Am.Ch., ambulacral channel ; B.Tf., channel for the branch of 

 the radial water-vascular canal to the tube-foot ; P., proximal direction ; D., distal direction, x 30. 



The simple flooring-plate character of the ambulacralia is shown in Text-fig. 160. 

 The same ossicles in apical view are shown in Text-fig. 164, p. 227. The ambu- 

 lacralia near the mouth are but little differentiated (Text-fig. 163, p. 227). 



1. Palasterina primaeva (Forbes). Plate XV, figs. 5 — 7; Plate XVII, fig. 3; 

 Text-figs. 30 (p. 37), 138 (p. 195), 157—164. 



1848. Uraster primxvus, Forbes, Mem. Geol. Surv. Gt. Brit., vol. ii, pt. 2, p. 463. 



1849. ., „ Forbes, Mem. Geol. Surv. United Kingdom, dec. i, p. 2, pi. i, figs. 2a, 2b. 

 1851. „ )r / Forbes in McCoy, Brit. Palaeoz. Foss., p. 60. 



1851. Palasterina primxva, McCoy, loc. cit., p. 59. 



1854. Uraster primsevus, Murcbison, Siluria, p. 221, fig. 39. 



1876. „ „ Quenstedt, Petrefakt. Deutschl., 1, iv, p. 74, ph xcii, fig. 35. 



1893. Palasterina primaeva, Stiirtz, Verbandl. Naturhist. Ver. preuss. Rlieinb, Jahrg. 50, p. 44. 



1899. „ „ Stiirtz, loc. cit., Jahrg. 56, pp. 214, 224. 



1899. Palxasterina primxva, Gregory, Geol. Mag. [4], vol. vi, p. 349. 



1910. Palasterina primxva, Schondorf, Jabrb. Nassau. Ver. Naturk., vol. lxiii, pp. 220, 243, 250. 



1913. Palxasterina primxva, Spencer, Introductory Section to this Monograph, pp. 37, 38, Text-fig. 30. 



1914. Palasterina primxva, Schuchert, Fossilium Catalogus, Animalia, pt. 3, pp. 31, 44. 



1915. „ „ Schuchert, Bull. 88, U.S. Nat, Mus., pp. 149, 151, 152, 153. 



