PLATE VI. 



UlNTACKINUS SOCIALIS. InTERBRACHIAL ArEAS AND IRREGULARITIES. 



(Interbracliials indicated by shade lines right to left downwards ; intersecundi- 

 brachs, left to right ; iuterpinnulars, vertical.) 



Fig. 1. Maximum specimen, dicyclic ; with 5 iBr plates in one area, and 8, without any 

 enclosed plate, in another. Specimen No. 43. 



" 2. Large specimen, dicyclic; with 17 and 20 plates in iBr areas, and 3 plates in lowest 



range ; interpinnulars extensively developed. No. 53. 



" 3. Medium specimen, dicyclic; with IBB unequally developed; 6 and 7 plates in iBr 

 areas. No. XXXVI a. 



(Enlarged figure of base of this specimen: PI. II., Fig. 8, supra.) 

 " 4. Small specimen, monocyclic ; with 5 and 6 plates in iBr areas, showing int>rease by 



intercalation in the middle. Collection Kansas University. 



'• 5. Large specimen with double centrale and one infrabasal ; plates of iBr areas vary- 

 ing from 9, without any enclosed plate, to 22, with several enclosed; 2 to 3 plates 

 in lowest range ; one iBr passing down between two radials and meeting truncated 

 basal. (The same thing occurs in a perfectly dicyclic and a monocyclic specimen, 

 Nos. LXVI a and b.) Interpinnulars present. No. 52 a. 



" 6. Large specimen, monocyclic ; with 10 to 23 plates in iBr areas ; 2 to 3 plates in 

 lowest range ; iBr in 3 areas passing down between radials and truncating 3 

 basals. No. 61. 



" 7. Large specimen ; the intersecundibrachs in one ray replaced by a large fixed pin- 

 nule, indicated by crossed lines. No. 1. 

 " 8. Medium specimen, monocyclic; the ill Br plates and one arm branch wanting in 

 one ray, — a large pinnule, marked by a dotted line, originating upon one bifur- 

 cating face of IBro. Part of No. XIV c. 

 " 9. Large specimen, with an extra pinnule-bearing arm developed in place of the 

 second fixed pinnule of the left ramus of the ray, —indicated by dotted line. 



Part of No. X e. 

 (All figures natural size. Figs. 8 and 9 by Mrs. Ricker; 4 by Mr. Syd. Prentice; 

 the others by Chapman.) 



