366 CEYLON PEARL OYSTER REPORT. 



Arcania quinquespinosa, ALCOCK and ANDERSON, 1894 A.2, p. 266. 



Locality : West of Periya Paar, 17 to 24 fathoms, one specimen. 



Description: Adult female, C.I. = 11*00 (includes frontal lobes, but not posterior 

 spine); C.b. (without spines) ^C.l. = 1'05; lateral spine 1. -f-C.l. = 3*41 ; Ch.l. -5- C.I. 

 = 2*23 ; F.I. - H.I. = 1*50. The pair of postero-lateral granules is present. 



Arcania erinaceus (FABRICIUS), 1787 A.2, p. 268. 



Localities : Pearl banks, Gulf of Manaar, two specimens (a, o) ; coral reefs, Gulf 

 of Manaar, one specimen (b). 



Description (measurements as in A. quinquespinosa) : 



A difference between the adult male and the adult female above is the presence in 

 the latter of a median longitudinal line of hair on the ischium of the external 

 maxilliped. 



Arcania tuberculata, BELL, 1855 A.2, p. 268. 



Locality: Pearl banks, Gulf of Manaar, two specimens (a, b). 



Description: C.I. C.b. -f C.I. Ch.l. + C.I. F.I. 4- H.I. 



(a) ovigerous ? . . . 9'50 0'89 1'18 0*77 



(6) ovigerous ? . . . 10'25 0'88 1'17 0'85 



Arcania pulcherrima, HABWELL, 1879 A.2, p. 269. 



Localities : Trincomalee, one specimen (a) ; coral reefs, Gulf of Manaar, one 

 specimen (b). 



Description: c.l. C.b. -f C.I. Ch.l. -=- C.I. F.I. -j- H.I. 



(a) young c? .... 8'00 1'09 2'06 0'82 



(b) ovigerous ? . . . 1075 1'09 2'16 077 



There are in both specimens 14 tubercles on the dorsal surface of the carapace in 

 addition to the 10 marginal prominences. 



Ixa cylindrus (FABRICIUS), 1787 A.2, p. 271. 



Localities : Aripu Reef, one specimen (a) ; pearl banks, Gulf of Manaar, one 

 specimen (b). 



Description (lateral spines included in C.b.) : (a) ad.<j. (b) ad. non-ov. ? . 



C.I 14-50 1675 



C.b.-j-C.L 2-83 2-88 



