12 Bulletin Vanderhilt Marine Museum, Vol. V 



margin is cut by a median V-shaped sinus, on either side of which 

 there is a triangulate, acuminate tooth, emphasized by a median longi- 

 tudinal carina ; the inner lateral margin set with about twenty articu- 

 lated teeth, another such tooth at the apex of the tooth; near the 

 proximal end of the outer lateral margin of this large tooth is a small 

 incision, in which is situated an articulated small tooth, and just 

 beyond this at the extreme base of this tooth is another small sinus 

 and an articulated spine; beyond this there is on either side a large 

 acuminate tooth with a median longitudinal blunt carina that extends 

 back three-fourths of the length of the telson ; the proximal two-thirds 

 of the outer lateral margin of this tooth is carinate, the carina widest 

 proximally and tapering gradually without an acuminate apex. 



Typical chiragra (Fabricius). 



One specimen, 33.5 mm. long, taken on coral reef at Anaho Bay, 

 Nuka Hiva Island, Marquesas Islands, August 10, 1931. 



This specimen corresponds to the preceding specimen in orna- 

 mentation except that the Anaho Bay specimen has two short tubercles 

 or carinae bordering the distal end of the median tubercle on the 

 proximal elevated portion of the telson and the second big tooth of 

 the telsonic margin is reduced in the present specimen to a rudi- 

 mentary tooth consisting of the tip of the carina and has no sinuses 

 or rounded process at its outer base; the third telsonic tooth is also 

 very rudimentary, consisting of only a denticle-like tip of the lateral 

 carina. 



One difference is to be found on the sixth abdominal segment, 

 namely: the outermost triangulate tubercle is dorsally cut by an 

 oblique carina that terminates in a denticle about midway the outer 

 lateral margin of the sixth tubercle, having the appearance of a 

 smaller triangle superimposed upon the sixth tubercle. The rostrum 

 is of the type having the outer angles rounded, but the frontal margin 

 distinctly excavate on either side of the rostrum, thus emphasizing 

 the outer angles. 



Another young specimen, about 25 mm. long, taken on Venus 

 Point Reef, Tahiti, Society Islands, August 5, 1931, differs as follows : 



As is to be expected in a very young specimen, the six longitudinal 

 tubercles of the sixth abdominal segment are less elevated and their 

 respective tips more acuminate than is the case in larger specimens. 

 The telson differs from the one described above in only two items: 

 (a) On either side of the median carina and opposite its distal end 



