34 EXPLANATION OF THE PLATES. 



spines ; the madreporic shield, and the strong, upright tentacle-spines. The first pore, outside 

 the mouth-slit, has a small tube but no spine. From the pores on either side of the madreporic 

 plate may be seen protruding the small tentacle covered by two spines. Fig. 54, ^, a tentacle- 

 pore with its thi'ee spines mounted on a granulated ridge. Fig. 55, ^-, tip of an arm I'olled on 

 itself; there are, as yet, no granules or small spines; but the curved tentacle-spines are formed. 

 Fig. 56, ^, a joint close to tip of arm. The ridges have two rows of granules, each bearing a 

 minute jointed spine which is usually folded down, the whole fitting together like fingers of two 

 hands. The intermediate sunken space is covered by three rows of granules. Below are seen 

 the large tentacle-spines (q), hooked at the end and covered by thick skin ; on the base of the 

 exterior one are two little spines similar to those of the granulated ridges above. 



Astroschema leeve, var., Figs. 57-59, from original in the Garden of Plants. Fig. 57, 

 ^, under siuface of a dried specimen. The mouth-angles have only teeth. The first pore has no 

 scale ; the second, one. The gi'anulation in this figure and the next is made too coarse ; there 

 should be twelve or fifteen grains in the length of G"""-. Fig. 58, f, upper surface, showing its 

 regular division in lobes with curved margin, and the arm joints as successive swellings. Fig. 

 59, ^, interbrachial space seen horizontally from without, exhibiting the vei-tical genital open- 

 ings at the inner angle. The specimen varies from the t^-pe in having a finer disk-granulation. 



Ophiothela isidicola, Fig. GO, *^-, to show the relation of arm-spines (p) and booklets (p') 

 to the side arm-plates (i) among Opbiuridse. 



PLATE V. 



Outlines of the mouth-angles, mouth-shields, and under arm-plates of twenty-four species of 

 Amphiurn. to exhibit the leading forms. The Amphiurcr, in the restricted sense of Ljungman, 

 are put first (Figs. GI - G8), to wit, those which have only four papilla? to each angle, while the 

 tentacle-scales of the first mouth-tentacles are seen higher uji. Then follow species that have 

 six or eight papilla; to each angle (AmphipJiolis Ljn.), among which will be noticed a great variety 

 in size, form, and relation of parts. Between Figs. 68 and G9 would naturally come ^-1. anomala, 

 PI. IIL Fig. 2G, an intermediate form, which satisfies me that there is no reason for cutting the 

 old genus Amphiura in two. Fig. 68 is from an older and larger specimen than Fig. 35, 

 Plate in. 



