490 



evenly arched. Abdomen compressed into a keel, its profile 

 more or less evenly arched from the mouth to the vent. A 

 very long compressed spine above the middle of each eye is 

 directed upward, and sometimes slightly forward. Two 

 similar but smaller spines are present on each side of the 

 back. Another on the middle of the side, well behind the 

 pectoral fin. Lower lateral ridge obsolete, its usual position 

 indicated by two or three spines; the first below the posterior 

 base of the pectoral fin, the last below the base of the dorsal 

 fin, and a smaller one, usually present, midway between these 

 two. 



Carapace uniformly granular, its scutes not clearly 

 defined. Abdominal surface more or less deeply and irregu- 

 larly grooved. Imperfect scutes are present behind the dorsal 

 and anal fins, and on the upper and lower surfaces of the end 

 of the caudal peduncle. Anterior dorsal and anal rays very 

 slightly produced in some specimens, forming a distinct angle 

 to the marofins of the fins. 



Colovr. — Entire carapace and tail ornamented with 

 polygonal spots and paired brownish bars on a light ground- 

 colour of pale-blue, white, or pale-yellow. The sides of the 

 snout bear more or less numerous oblique bars, which also 

 extend over the sides of the abdomen, where they are some- 

 times irregular and vermiculate. The polygonal spots on the 

 sides of the carapace form distinct rows in some specimens, 

 but are more irregular in others, and each usually has a 

 central blue spot. Caudal peduncle and bases of dorsal and 

 anal fins with dark paired stripes, separated by narrow blue 

 streaks, and disposed more or less horizontally ; the inter- 

 spaces are pale-blue or white. Anterior portions of dorsal 

 and anal fins darker. Caudal with blue inter-radial bars, 

 which are symmetrically disposed and connected by an intra- 

 marginal series of loops; these bars are defined by darker 

 lines, and vary in form; they are scarcely developed in our 

 smallest specimen. 



Two young specimens, 87 and 93 mm. long, respectively, 

 differ in having the sides of the carapace marked with brown 

 bars, similar to those on the snout, abdomen, and tail, instead 

 of being ornamented with polygonal spots. The caudal fin 

 is almost or quite plain. 



Described from fourteen specimens, 87-114 mm. long, 

 the largest of which is figured. 



Kent regarded this species as the male form of A. aitrita, 

 though he offered but little proof of his contention. We are 

 unable to examine the sexual organs of our specimens, and 

 in the absence of more definite information prefer to keep the 

 two forms separate. 



