1890.] G. M. Giles — Descriptions of new Indian Amphipods. 63 



It follows, therefore, that the quantity 



W (ac - J2)3 



O aH-3abc+2b* 

 is an invariant for the given cubic and its aberrancy curve. 



If we seek the common points of intersection of the two cubics, 

 we find on subtracting the equations 



(ace + bf> = 

 which shews that the two cubics have only one common point of in- 

 tersection which is the point of inflexion for both ; the coordinates of 

 the point are 



b G 



® - - --, y--k 

 a a* 



VI. — Natural History Notes from H. M. Indian Marine Survey Steamer 

 'Investigator,' Commander Alfred Carpenter, R. N, D. S. O., 

 commanding. — No. 15. Descriptions of seven additional neiv Indian 

 Amphipods. — By G. M. Giles, M. B., F. R. C. S., late Surgeon-Natu- 

 ralist to the Survey. 



[Received and Read November 6th, 1889.] 



(With Plate II.) 



Before proceding to the description of the species now described, 

 I have to make a correction in my last paper read on February 1st, 1888. 



In that communication, I described, under the name of Ooncholestes 

 dentallii, gen. et sp. nov., a curious corophiid which inhabits deserted 

 dentalium shells ; remarking that I believed that such a habit had not 

 beeu previously noted in an amphipod. I find, however, I was in eri'or 

 in this matter, as, while searching for references to species which might 

 be identical with those described in the present paper, I came across 

 a description of a Norwegian species which is certainly congeneric and, 

 like the Indian species, inhabits deserted dentalium shells. Sars (Forh. 

 Vidensk.-Selsk. Christiania, 1882, No. 18, pp. 113, Part VI, fig. 7) 

 describes this species as Siphonoecetes pallidas. 



I do not see, however, how either Sars' or my species can be in- 

 cluded in Siphonoecetes without unduly straining Kroyer's definition 

 of the genus in Nat. Tidskr. I, p. 491. In the two species under consi- 

 deration, the 1st and 2nd gnathopoda, instead of being subequal, present 

 a very marked difference of size ; and again, the eighth thoracic appen- 

 dages are very long, instead of the 6th, 7th, and 8th being " very short." 

 My species too wants the double hook to the single ramus of the last 



