PER I ASTER TENUIS. 209 



Station 3431, off Altata, Gulf of California, 995 fathoms. Lat. 23 59' N. ; 

 Lung. 108' 40' W. Bottom temperature, 37°. Lt. br. m. Glob. 



Station 3436, south of Guaymas, 905 fathoms. Lat. 27 34' N. ; Long. 

 110° 53' 40" W. Bottom temperature, 37 .2. Br. m. bk. sp. 



Station 3437, 50 miles south of Guaymas, 628 fathoms. Bottom tem- 

 perature, 40". Bn. m. bk. sp. 



Bathymetrical range, 146-995 fathoms. Temperature range, 51. 2-37°. 



Periaster D'Orb. 

 Periaster tenuis A. Ag. 



Periaster tenuis A. Ag., Bull. M. C. Z. 1898, XXXII, No. 5, p. 82, PI. XI, figs. 6, 7. 

 Plates 103, figs. 5 7; 104 ; 105, figs. IS. 



This species is much flatter and less cylindrical (PI. 104, fig. 3) than 

 P. Umicola from the Gulf of Mexico. It has no anal fasciole. The peri- 

 petalous fasciole is wide (Pis. 103, fig. 6; 104, figs. 2, J; 105, fig. ..'), covered 

 by prominent miliaries. The actinal plastron is elongated (Pis. 104, figs. 

 1, 4; 105, fig. l), and the tuberculatum of the test is close (Pi. 104, fig. 3). 



On coming up in the trawl the color of the test is light brown, though 

 it is found at considerable depths, nearly 1800 fathoms, depths at which 

 the prevailing tints and colors of the Echini found there are pinkish to 

 dark violet. Aerope and Phrissocystis are similar exceptions: they are 

 both yellowish and brown, and are found, the one at over 1000 fathoms, 

 the other to nearly 1800 fathoms. 



Seen from the abactinal side the Panamic species is only slightly elongate, 

 the labium narrow and very prominent (Pis. 104, figs. 1, 4 ; 105, fig. 1). 

 The apical system is slightly anterior, the petals broad, sharply constricted 

 at the peripetalous fasciole (PI. 105, fig. -), the odd anterior ambulacrum 

 narrow. The vertex is near the anterior line of the peripetalous fasciole 

 (PI. 104, fig. 3); from this the test slopes very gradually to the anterior 

 extremity, which is rounded, the ambitus passing gradually to the actinal 

 surface (PI. 104, fig. S). The posterior extremity of the test is truncated, 

 sloping sharply from the vertex to the ambitus, where it forms a rudimen- 

 tary posterior snout (PI. 104, fig. 3). 



The labium and sternum of this species (PI. 105, fig. 1) are much longer 

 and narrower than in P. Umicola, and the bare ambulacra flanking the 

 sternum fully twice as wide as in the Mexican species. 



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