244 MR. W. PERCY SLADEN OK THE 



the plate. Behind the inner or furrow-series of ambialacral 

 spines are 3-5 small granules, arranged in a slightly curved line, 

 which appears to follow the rounded margin of the adoral ex- 

 tremity and the outer side of the adambulacral plate. The most 

 adoral of these granules show a tendency to develop the flat and 

 pointed form of the ambulacral spines ; and there is little doubt 

 that they are the representatives of an outer or secondary series. 



Mouth-plates large and prominent, each curving down coulter- 

 form until the margins which fall in the median line are at right 

 angles to the plane of the actinal surface. The prominent 

 median keel thus produced slopes with a regular curve ad- and 

 aborally, its longitudinal profile being almost semicircular. The 

 median suture is not closed, but rather widely open, and expands 

 towards the aboral extremity of the plates and exposes a portion 

 of the odontophore. Each plate bears a short, robust, conical, 

 pointed spine at its innermost extremity, the companion spine 

 of the adjoining plate standing parallel. There is thus a pair of 

 short, but conspicuous mouth- spines directed towards the centre 

 of the peristome from each mouth-angle. The remaining mouth- 

 spines are 6 in number and are uniform in size and shape with 

 the ambulacral spines, and are arranged along the margin of the 

 plate which abuts on the furrow, A few prominent granules 

 are present on the surface of the mouth-plates, but do not, in the 

 specimen under description, appear to be arranged in any definite 

 order. 



The ventral interbrachial areas are large and extensive, flat, 

 and covered with oblong squamiform plates. On the outer por- 

 tion of the area these plates are about twice as broad as long, 

 and are arranged in columns parallel with the median interradial 

 line. In the neighbourhood of the mouth-angle and adjoining 

 the adambulacral plates the ventral plates become larger and 

 altered in form and appear independent of the column-series. 

 The ventral area is covered with a very fine and almost imper- 

 ceptible membrane, plates and membrane together being so thin 

 that traces of the internal organs of the starfish can be seen 

 through them. A number of small irregularly disposed granules 

 are distributed over the area, but seldom more than 2 or 3 on a 

 plate, and often wanting. The imbrication of the plates appears 

 to be very slight in this species, and is perhaps only present in 

 the outer part of the areas. 



