I v.— R E M A R K A B L E C A vS E S OF VARIATION. 



By R. E. Li<OYD, M.B., B.Sc, Capt., I. M.S., formerly Surgeon 

 Naturalist, Marine Survey of India. 



I. — SouiivivA Investigatoris. 



An^^one who examines large numbers of animal organisms 

 and attempts to fit them into the established specific groups, must 

 be sometimes in doubt as to the propriety of placing certain of 

 them into any particular group. This doubt is by no means always 

 felt. As a rule organisms can be readily placed in established groups, 

 or new ones or species defined for their reception. Occasionally, 

 however, a number of individuals are found living together in the 

 same environment, and resembling one another so closely in most 

 respects that we hesitate to place them in more than one species, 

 although in certain particular features they differ wideh', one from 

 the other. To establish several species for such a collection seems 

 most inappropriate, for by so doing the offspring of even the same 

 ])arents might be described as different species. If certain of the 

 Crustacea here described had been taken from widely separate 

 localities there is no doubt that they would have been regarded 

 as separate species. Animals which show such a wide range of 

 variation are rare in comparison with ones showing a limited range, 

 but they undoubtedly occur. They are perhaps less uncommon 

 among the marine fauna of tropical seas than in other environments. 



During the early part of 1906, the R.I.M. Survey ship " Inves- 

 tigator" trawled at ten stations along the south-west coast of Arabia. 

 At one of these (Lat. 15° 8' 30" N. Long, ^i"" 52'-i5" E.). from a 

 depth of no fathoms, a very large number of a species of Squilla 

 was obtained. It is much to be regretted that the interesting 

 features of the species were not recognised at the time of their 

 capture, and that onh' some twenty complete specimens were 

 retained. vSeventeen of these are now available for examination in 

 the Indian Museum ; this number, however, is quite sufficient 

 to illustrate the remarkable variability of the species. 



The seventeen specimens resemble one another very closely 

 in all parts of their outer structure with one exception. The 

 number of spinous teeth on the dactyle of the raptatorial claw 

 varies from ten to eighteen among this small collection of seven- 

 teenjindividuals. Furthermore, as regards this appendage, they 

 show_^no less than eleven different types displayed in the following 

 table ; — 



