150 Memoirs of the Indian Museum. [Vol. IV, 



ii. Telson with three circular bosses ; spinules with recurved points 



directed backwards . . . . . . . . hystrix, p. igo. 



b. With long spines .. .. .. .. . . spinosissimus,p. 191. 



II. Mandibular palp absent; inner margins of inner uropod and of ultimate 

 segment of outer uropod bearing large spines [numerous slender dorsal 

 spines at distal end of telson]. Group IV. .. .. .. acanthurus, p. 193. 



Gonodactylus chiragra and its allies. 



There is considerable difference of opinion respecting the' precise relationships 

 between Gonodactylus chiragra and its near allies oerstedi, acutirostris , demani, spinosus, 

 espinosus, festae, glabrous and graphurus, and I^anchester, whose important paper on the 

 subject (1903) deserves careful consideration, holds that all must be regarded as varie- 

 ties of a single species. In this view he has not been followed by more recent authors, 

 and a careful survey of the large collection in the Indian Museum seems to show that 

 he has omitted to lay sufficient emphasis on the more outstanding features of the case. 



The variation shown in these species of Stomatopoda presents problems of rather 

 unusual interest and before any final conclusions can be reached much work based on 

 living material must be undertaken; it is, I believe, only by direct observation on the 

 post-larval growth, habits and associations that a true estimate of the relationships 

 of the various forms can be reached. The variation in these species seems to find no 

 parallel among other Stomatopoda, many of which,, notably the species of Squilla 

 belonging to the S. oratoria group, are remarkable for the constancy of small and seem- 

 ingly trivial characters. 



The outstanding features of the variation in the chiragra section of the genus 

 Gonodactylus appear to me to be as follows :— 



Distributed throughout the Indo-pacific region, occurring on rough ground, in 

 rock-pools or on coral reefs, a form which may be called Gonodactylus chiragra, s.s., v 

 is abundant. In the characters afforded by the ornamentation of the last abdominal 

 somite and telson a large amount of variation may be found ; the keels with which 

 these segments are furnished may be swollen or narrow and may or may not terminate 

 in spines ; the median carina on the telson is moreover simple and linear or it may bear 

 short lateral branches at its distal end and so take the form of an ' anchor.' Between 

 the various forms every shade of intermediate can be found. Intermediate forms in 

 any selected character are also commoner than those which exhibit it in an extreme 

 development, but in their turn are less abundant than those which conform more or less 

 closely with the prevailing type. 



Now in examining large series of examples one feature is predominant in the Indian 

 Museum collection : the variation shown among large examples (70 mm. or more in 

 length) is very much less than that found in small specimens (60 mm. or less in length), 

 and it is further to be noticed that the individuals which in Lanchester's opinion formed 

 connecting links between this form and its allies are also characterized by their ex- 

 tremely small size. 



1 The characters employed for the separation of this form from its allies are shown in the key 

 on p. 147. 



