I913O S. Kemp : Crustacea Stomatopoda of the Indo-Pacific Region. 19 



It will be noticed that the palp in this genus is either well formed and composed 

 of three segments, or wholly absent ; no instances of a one or two-segmented palp 

 have been observed. 



The inter-relationships of the Indo-pacific species cannot be traced with any great 

 degree of satisfaction. 5. raphidea and 5. annandalei , in the possession of large fixed 

 spines on the penultimate segment of the raptorial claw, stand apart from all the rest, 

 and the latter fall into two groups characterized by the structure of the fifth thoracic 

 somite. The first of these groups contains the small-eyed species originally placed 

 il), a separate genus, but linked to the more normal types by such forms as 5. chlorida, 

 S. fasciata, S. lata and 5. gilesi. It also contains the highly-specialized deep-water 

 section, comprising S. leptosquilla and tenuispinis and a few isolated species, 5. scorpio, 

 S. armata and S. mantoidea. The second group, which in point of individual abund- 

 ance greatly outweighs the first, contains a number of closely- allied species that fall 

 into three sections, typified respectively by 5. laevis, S. quinquedentata and 5. nepa. 

 In addition it includes four highly-specialized forms, 5. investigator is , S. costata, S. 

 multicarinata and S. supple x. The last is perhaps a remote connexion of S. laevis ; 

 the other three appear to be early offshoots of the original nepa and quinquedentata 

 stock ; but in each of them specialization has progressed on different lines. 



The species of Squilla for the most part inhabit shallow water and seem to prefer 

 sandy or muddy ground. They construct burrows ; but as they frequently leave them 

 in pursuit of prey, they are often taken in abundance in fishermen's nets. Giesbrecht 

 (1910) gives a valuable account of the bionomics of Squilla mantis in the Mediterranean. 



Brooks (1886, p. 168) states that ' ' Squilla stridulates by rubbing the serrated 

 spine of the swimmeret across the serrated ridge on the ventral surface of the telson. 

 The noise which is thus made under water can be clearly heard above the surface." 

 This observation was made on Squilla empusa. Giesbrecht (1910, p. 201) found that 

 Squilla mantis produced sound in a similar way, but only when it was grasped with a 

 pair of forceps. From the structure and relative position of the parts the method of 

 sound-production is not very clear ; but most Indo-pacific species possess a lateral 

 carina on the under surface of the telson as in 5. empusa and S. mantis, and it is prob- 

 able, therefore, that stridulation is effected in the same way : my efforts to induce 

 living Squilla to produce sound have, however, proved quite unsuccessful. Wood- 

 Mason unfortunately gives no reason for his choice of stridulans as. a specific name and 

 his specimens do not seem to possess any special structural distinctions which would 

 furnish an explanation. 



Key to the Indo-pacific species op Squilla. 

 The following key to the Indo-pacific species of Squilla is based on adult 

 characters ; great caution should be used when employing it for specimens under 

 40 mm. in length. 



I. Upper margin of propodus of raptorial claw with a series of fine and 

 even pectinations in addition to a few movable spines at proximal end. 



