Verrill, Notes on Radiata. 579 



ECHINOIDEA. 



Quite recently I have had an opportunity to compare specimens of 

 most of the following species with those in the ^luseum of Compara- 

 tive Zoology, in company with Mr. A. Agassiz, who, while in Europe 

 last year, took pains to carefully examine nearly all the typical speci- 

 mens contained in European museums, and in many cases brouc/ht 

 home specimens identified by direct comparison. Therefore I am able 

 with the approval and through the courtesy of Mr. Agassiz, to correct 

 a few erroneous identifications previously made by him, together with 

 others made by myself in the earlier part of this volume. Other spe- 

 cies, described since the earlier articles on the Echinoderms of the 

 Pacific coast were printed, have been introduced in order to render 

 the work more complete. 



Cidaris Thouarsii Vai. (p. 294). 



Numerous specimens were sent by Capt. Pedersen from La Paz. 

 They show great variation in form, in addition to that due to dif- 

 ference of age. Several specimens give the following measurements : 



Diameter, (inches) 2-10 2-05 2-00 1-55 1-50 ]-35 1-30 



Heiglit, 1-30 1-35 1-50 -85 -80 -75 -75 



Actinal area, -85 -90 -80 -73 -70 -64 -55 



Abactiiial area, -70 -70 '68 -58 -56 -50 -43 



Anal region, -38 -40 -33 30 -30 -28 -22 



Astropyga depressa Gray, Proc. Zool. Soc. Lond., xxiii, p. 35, 1855. 



Astropyga venusta Verrill, these Trans., p. 296; Amer. Jour. Sci., xlix, p. 99, 1870. 



Mr. A. Agassiz, who has recently examined Dr. Gray's type and 

 brought home a specimen idenitfied by comparison with it, has com- 

 pared the latter with specimens sent by me, and regards them as 

 identical with the A. depress^ of Gray. The latter Avas described 

 from a young specimen, but considerable changes take place, especially 

 in the arrangement of the tubercles, during its growth, and even after 

 it becomes two or three inches in diameter, as may be seen from the 

 original descriptions of small and medium sized specimens (p. 29(j). 



Capt. Pedersen sent from La Paz two fine large specimens, about 6 

 inches in diameter, and I have seen a similar one in the Museum of 

 the Chicago Academy, collected at San Salvador by Capt. Dow. 



These large specimens have 12 to 14 vertical rows of large, nearly 

 equal interambulacral tubercles on the lower side ; the first row from 

 the ambulacra extends on the upper side to within three or four plates 

 from the summit ; between this row and the ambulacral pores, a row of 

 secondary tubercles is introduced, which commences a short distance 



