338 bulletin: museum of comparative zoology. 



occasionally, by what appears to be splitting, or by intercalation 

 there are 7 or even 8 plates, on a segment instead of six. Inter- 

 brachial areas below covered by a pavement of closely set, small 

 thick plates. Genital slits, 2 in each area, very small, starting close 

 to oral shield and not exceeding the first arm-segment, bordered 

 abradially by 4-6 small but noticeable papillae. Oral shields mod- 

 erate, distinctly wider than long, somewhat triangular, except the 

 madreporite which is larger and more tetragonal. Adoral plates 

 straight and narrow, 3 or 4 times as long as wide, fully meeting within. 

 Oral plates small and indistinct. Oral papillae, 5 on a side and one 

 at apex of jaw; penultimate largest, flat and wide. First under 

 arm-plate, small, diamond-shaped, wider than long; succeeding 

 plates, pentagonal, almost or quite as long as wide, little or not at all 

 in contact, distal margin a little convex, adjoining lateral margins 

 concave. Side arm-plates small, but meeting below except near 

 disk ; each carries 2 short, thick, bluntly pointed arm-spines, of which 

 the lower is the longer but does not equal a segment. Tentacle- 

 scales single, rather large, bluntly pointed. Color, dry, pale olive- 

 gray above, the arms very faintly and irregularly banded; beneath 

 uniformly light buff. 



This species is obviously different from any other species of the 

 genus except 0. huttoni of New Zealand, and Farquhar's excellent figures 

 make it possible to compare it closely with that nearly allied species. 

 I have decided that the two must be different because of the number 

 and arrangement of the upper arm-plates. All three of the Australian 

 specimens, though they range in disk-diameter from 5 to 10 mm., 

 agree in the fundamental plan, already described by which these plates 

 are arranged. In 0. huttoni, however, there are 9 or 10 plates on each 

 segment, including a distal series of three or four plates which is 

 lacking in the Australian specimens. I am inclined to lay consider- 

 able stress on this because comparison of specimens of the other three 

 species, shows that there is for each member of the genus a character- 

 istic plan. In 0. csmarki, it is similar to that of 0. hispinosus but the 

 proportions of the plates are different. In 0. imbricatus the number of 

 plates on a segment rises to a dozen or more, while in 0. japonicus 

 there may be fifteen or even seventeen. The scaling of the disk is 

 different in 0. hispinosus from what it is in 0. huttoni as there is no 

 regular arrangement of smaller plates around larger ones. Under 

 the circumstances, the Australian Ophioplocus may be considered 

 distinct from that of New Zealand until direct comparison proves 

 them to be the same. 



