152 PANAMIC DEEP SEA ECHINI. 



difficulty, owing to the great size of the intercalated or intruding inter- 

 ambulacral plates, in considering them as the abactinal plates of a smaller 

 series preceding them. 



The primoridial interambulacral plates in contact with the actinostome 

 vary but little in size, Fig. li 14-. The labium is, owing to its isolation from 



the sternum, lanceolate. 



In Plexechinus (PI. 59, fig. 3), as in Urechi- 

 nus (Pis. 58, fig. .7; 73. fig. /), the second plate 

 of the lateral ambulacra is a double plate. 



The Urechinid type of the odd anterior am- 

 bulacrum and of the adjoining interambulacra 

 Fig. 220. Ubechinus Naresianus. of I'lexeeliinus is well seen on comparing Fig. 



214 and Fig. 220, which represent the odd am- 

 bulacrum of PI. ductus and U. Nuresianus, with the odd interambulacrum of 

 other Urechinids, such as Cyst echinus Looeni, with Spatagocystis, Echino- 

 crepis, and Pourtalesia, Figs. hi:!. 165, and 169. In the Urechinids the 

 second plates of the paired interambulacra are double, while they are single 

 in the Pourtalesiae. 



Station 3424, off Tres Marias, Gulf of California, in 676 fathoms. Lat. 

 2P 15' N.; Long. 106 23' W. Bottom temperature, 38 . Gy. s. blk. s. blk. 

 sp. glob. 



ANANCHYTID31 Alb. Gins. 

 URBCHiNlDiE Lambert (emend.) 



Urechinus A. Ag. 

 Urechinus giganteus A. Ag. 



Urechinus giganteus A. Ag., Bull. M. C. Z. L898, XXXII, Xo. 5, p. 79, PI. VIII, tigs. 7. 8. 



Plates 72 ; 73 ; 74, figs. IS. 



From Station 3431 two large specimens of Urechinus were collected 

 (PI. 72), far larger than any specimens of the genus hitherto obtained by 

 the •• Challenger " or the " Blake." The smaller specimen measured 80 mm. 

 in length. 63 mm. in width slightly posterior to the apical system, and 

 37 mm. in greatest height. The larger specimen measured 93 mm. in 

 length, 80 mm. in width, and 39 in height. The outline as seen from 

 above or below is ovoid (PL 72, figs. 1, 2) ; the larger specimen is propor- 



