MUSEUM OF COMPARATIVE ZOOLOGY. 269 



two parts on the succeeding joint, and lias a couple of supplementary pieces with- 

 in. The two parts are still mure diverging on the next joint, j; the large side 

 arm-plate, ;', comes up toward the median line, and the upper arm-spine p is promi- 

 nent ; \"-. 



Fig. 13. A joint near the middle of the arm. The two parts of the upper arm- 

 plate, j, arc now completely separated by the intrusion of supplementary pieces, 

 which have increased to seven ; p, arm-spine ; i, side arm-plate ; \ a . 



Fig. 14. A joint at the base of the arm. The two parts of the upper arm-plate 

 j, instead of occupying the top, have been wedged apart by supplementary pieces, 

 until they are on each margin. The side arm-plates, i, have become small as com- 

 pared with the supplementary pieces, and the arm-spines,^?, a#no longer con- 

 spicuous ; X £: 



Fig. 15. Opinion squamosissima. Piece of arm near its tip, enlarged. The 

 outer joint bears a small, simple upper ami-plate ; the innermost one has also a 

 simple plate, j, outside which are two supplementary pieces, k ; on either side is 

 a large side arm-plate, ?', bearing a short spine. 



Fig. 16. A joint near the base of the arm. The upper arm-plate still occupies 

 the median line, j ; but the two supplementary pieces, k, have moved from a 

 position beyond, to one on either side of the upper arm-plate, and still another sup- 

 plementary piece has been formed in a line with the rest and lying on the margin. 

 The side arm-plate has become comparatively small, i, and has been crowded 

 clown on the side of the arm. 



Fig. 17. Opliiura cincrca. A joint near base of arm, showing the upper arm- 

 plate broken in several pieces, as is usual ; f. 



Fig. 18. OpTi iopholis aculcata. Two joints near end of arm showing the upper 

 arm-plate, j, with a row of grains or small supplementary pieces, only along their 

 outer margin ; f. 



Fig. 19. Two joints near the base, showing the same plates, ;', completely en- 

 circled by a close row of small pieces, which may be double on the sides ; f. 



Fig. 20. OpMont reis dubia. A joint near end of arm showing the simple up- 

 per arm-plate, j : - c r- 



Fig. 21. A joint near base of arm, with a small supplementary piece, k, on 

 each side of the upper arm-plate, j ; 2 1 Q . 



PLATE VI. 



Astmplnjton cacaoticum sp. nov. ; Astrophyton nudum sp. nov. ; Ophioplocus Es- 

 inarki sp. nov.; Opliioneplithys pludcrata sp. nov. ; Pcclinura scpi spi- 

 iiosa Mull. & Trosch. ; Opldomastix ftaccida sp. nov. 



Fig. 1. Aatropilvjton cacaoticum (from a dried specimen). A part of the 

 disk, fmm below, with outline of one fork of the arm, showing the distance of the 

 branches with approximate accuracy ; \. 



