156 Bulletin Vanderhilt Marine Mitseum, Vol. VII 



Technical description: The disk is rounded pentagonal, 

 moderately thick. The disk diameter of the large specimen is 35 

 millimeters, the arm length about 108 millimeters, the dorsal 

 width of the arm between the spines is 5 millimeters; length of 

 the arm spines (about the fifteenth somite, dorsal to ventral) 7. 5, 

 4, 3.4 millimeters, respectively. The abactinal surface of the disk 

 and interbrachial areas of the actinal surface are covered with 

 fairly coarse rounded granules. Where abraded, the scales be- 

 neath these granules are small, regularly overlapping, with convex 

 outer margins. The central mouth shield is longer than wide, 

 with the inner portion definitely narrower than the outer, bounded 

 by a rounded apex from which the slightly rounded lateral mar- 

 gins diverge posteriorly, their outer angles also rounded and the 

 proximal margin wide, also slightly convex. In the very young 

 specimen the central mouth shield differs from that of the large 

 specimen in appearing longer in ratio to the proximal border, 

 which in the smaller specimen has the outer lateral margins con- 

 verging very much to a narrowed proximal border, much as in 

 the specimens figured by M. Koehler (1905). The side mouth 

 shields are triangulate, each plate lying adjacent to the lateral 

 border of the central plate, with the inner apices separated. The 

 four teeth on each side of the jaw-angle are truncated, the first, 

 or outermost, being 1.5 times as wide as the second, which it 

 slightly overlaps, the second tooth similarly overlaps the narrower, 

 squarish third tooth which is nearly a third wider than the fourth ; 

 there are two smaller, subequal teeth at the apex of the jaw-angle. 

 The teeth papillae, about 18 in number, are set in three to four 

 series, extending downward and outward. There are four large, 

 flat, squarish teeth, of which the uppermost one is the smallest. 



The arms are a little over three times as long as the disk diam- 

 eter. The ventral arm plates are slightly wider than long, hexa- 

 gonal, with the distal margin widely convex, the paired lateral 

 margins concavely excavate anteriorly and posteriorly obliquely 

 convergent to the short, relatively straight proximal margin. In 

 this large Hawaiian specimen the proximal ten somites of the 

 arm occur within the radius of the disk and each somite bears only 

 three spines on each of these side arm plates. In each instance 

 these spines consist of two claviform and a third, dorsal, short, 

 tapered, cylindrical spine. Beyond this on the arm, the side arm 

 plates bear in irregular alternation four or three spines per 



