584 MR. W. PERCY SLADEN ON MIMASTER. 
enveloped in membrane. The structure of the abactinal floor and of the mar- 
ginal girdle is thus quite distinct in the two forms. Respecting the structure 
of the actinal floor, the description of Radiaster does not enable a comparison 
to be made. It is quite possible that the forms may be even more widely 
separated than I have supposed. 
I have named this very interesting species after Staff-Commander Tizarp, 
R.N., under whose command the “Knight Errant” cruise was conducted, 
and to whom science is largely indebted for many valuable services and con- 
tributions. 
Habitat.—Faeroe Channel, lat. 59° 33’ N., long. 7° 14' W. (“ Knight Errant” 
Dredging Station No. 4, August 10, 1880.) Depth, 555 fathoms. Bottom 
temperature, 45°°4 Fahr.; surface temperature, 57° Fahr. Sea bottom, mud. 
A single example. 
DESCRIPTION OF PLATE XXXIV. 
Fig. 1. Abactinal aspect of a ray of Mimaster Tizardi ; natural size. 
» 2. Actinal aspect of the same; natural size. 
, 3 Outline sketch of the whole starfish, seen from above, to show the marginal contour; 
one-third natural size. 
, 4. Outline sketch of the starfish, seen in profile; one-third natural size. 
, 5. Three adambulacral plates, showing the ambulacral spines, together with a portion of 
the adjacent ventral plates and their paxille ; magnified 5 diameters. 
6. A portion of the dorsal surface, showing the dorsal paxille and papulle; magnified 5 
diameters, 
, 7. A mouth-plate, seen in profile; magnified 5 diameters. 
