59C BRISSUS. 



ambulacra are larger than those adjoining the odd anterior ambulacra] 

 groove. The whole of the posterior part of the test above the ambitus is 

 covered by closely packed, smaller tubercles; the anterior furrow carries 

 along the median line only minute miliaries ; near the apex the test is covered 

 by a tuberculation similar to that of the adjoining parts <>(' the test near the 

 ambitus. The odd anterior poriferous zones are reduced to double pores, 

 vertically distant. 



The color (in alcohol) of specimens covered with spines was yellowish- 

 gray; the spines are slender, curved. 



Panama ; Gulf of California. 



BRISSUS. 



Brissus Ki.i-in, 1734, Nat. Disp. Ech. 

 (Sei Part II. p. 356,) 



Brissus carinatus 



! Spatangus carinatus LAMK., 1816, An. s. Vert., p. 30. 

 ! Brissus carinatus Gray, 1825, Ann. Phil., p. 9. 



PL XXP.f. i , ; PI XX V.f. 86, .; ; PI XXVI. f. 38. 



This species, which has a very wide geographical distribution, varies also 

 considerably, and its differenl stages of growth have been described as dis- 

 fcincl species The principal difference between this species and B. unicolor 

 consists in the outwardly curved course of the posterior half of the posterior 



lateral ambulacra, which are shorter than the anterior, if much curved ; the 

 more angular peripetalous fasciole, forming one deep re-entering angle in the 

 posterior interambulacrum, across the high rounded keel, which extends from 

 the apical system to the posterior extremity. In the anterior lateral ambu- 

 lacra the fasciole forms two deep re-entering angle-, crossing the narrow odd 

 ambulacrum at an obtuse angle. The posterior extremity is more obliquely 

 truncated than in B. unicolor. where it is nearly vertical. In young speci- 

 mens the test is more depressed | B. depressus) ; the keel not so prominent ; 

 the posterior extremity rounded, and the difference in the direction of the 

 lateral petals not marked, as it gradually becomes in older and larger speci- 

 mens. The test of dried specimens is frequently mottled; the central part 

 of the plates is dark, leaving the edge light or white. The width of the 

 peripetalous fasciole is greater in young and smaller specimens than in the 



