470 PAL,<EONTOLOGICAL REPORT OF GEOLOGICAL SURVET- 



Second radials five, divided two-thirds their length, swelling rapidly 

 from their junction with the first radials to the inferior end of the pseud- 

 ambulacral fields ; twice as long as wide, the branches increasing in 

 width from their junction with the interradials toward the base; ob- 

 liquely truncated above, the truncation being by a sigmoid line, (not 

 straight as is usually the case,) meeting and fitting upon the inter- 

 radials by a lap, being beveled from within, the beveled surface being 

 about three times as long as the thickness of the pieces ; abutting 

 squarely at their lateral margins against each other, two resting upon 

 the complete hexagonal fist radials, and the other three resting upon 

 the beveled sides and in the notches formed by the junction of the first 

 radials ; the line of j unction of the sides occupies the center of a deep . 

 elliptical grove. 



IntcrradUd pieces five, half as broad as long, (externally ;) angular- 

 ly pointed above, and roundly pointed below ; f as long as the second 

 radials ; within the body they are prolonged, and extended under the 

 second radials, and terminate in a long point on either side, forming 

 part of the wall of the pseudambulacral areas ; the centre is also ex- 

 tended downwards and pointed, laping uuder the suture, marking the 

 junction of the second radial pieces. 



The interradials are marked by fine striae, (lines of increment,) 

 which conform to the external form of the piece in its different stages 

 of growth. 



The first and second radials are also marked by lines of increment. 

 In the first radials the lines conform to the sides and upper margins of 

 the.pieces; the second radials are marked with lines extending entirely 

 around them, excspt around the margin of the fork, into which are 

 inserted the pseudambulacral fields. All the pieces are divested of the 

 epidermis and muscular coat. The trite' external markings are un- 

 known. 



Pseudambulacral areas extend from the mouth, at the centre of the 

 summit* a little below the centre of the length of the body, gradually 

 increasing in width by a curved line on either side from below up- 

 wards, to the centre, when they diminish in width until they reach the 

 summit, th«y are composed of a double row of thin plates, about- 

 twelve times as long as thick, aboujb: as; broad as long, joined, together 

 by their broad laces, terminafciflg ai, the centre margiiurf! the fields at a 



