THE CRUSTACEA 



The body (Fig. 186) is more or less flattened dorso-A'entrally. 

 The carapace is fused dorsally with at least two of the thoracic 

 somites, two others are represented by indistinct vestiges over- 

 lapped by its hinder edge, while the last four are free and com- 

 pletely developed. The lateral wings of the carapace project more 

 or less horizontally, roofing over on each side a widely open channel 



Squilla mantis, male, from tlie side, a', antenniile ; a", antenna ; p, penis ; sc, scale or 

 exopodite of antenna ; i/ii, th'-', th>^, first, second, and last thoracic appendages. 



within which lie the epipodites of the anterior thoracic appendages, 

 and which corresponds to the branchial cavity of other forms. 

 Anteriorly the carapace does not extend to the front of the head 

 (Fig. 187), leaving uncovered two movably articv^lated segments. 



Anterior part of body of Squilla mantis, from above, a', antennule ; a", antenna ; a.s, 

 antennnlar segment of head ; c, carapace ; o.s, ophthahuie segment of head ; r, rostral plate ; 

 sc, scale or exopodite of antenna. 



which carry respectively the eyes and the antennules, and which 

 are commonly regarded as representing the ocular (o.s) and 

 antcnnular (a.s) somites. A small rostral plate (r), movably 

 articulated with the front edge of the carapace, overlies the 

 antennular segment. 



That part of the head lying between the point of attachment of 

 the antennae and that of the mandibles is much elongated, formina: 



