The "dorsal organ" in Crustacea Malacostraea. 79 



Squilla. In S. mantis L. the median keel is considerably 

 widened and flattened above somewhat behind the bifurcation 

 and far in front of the mandible ; the widened, rather short part 

 has a very oblong depression, the bottom of which is a little 

 convex and looks as pricked feebly with a needle. In S. 

 raphidea F. the organ is conspicuous and nearly as in S. mantis. 



In S. Desmarestii Risso was found in two of four specimens 

 examined a small, circular, low depression with a rudimentary 

 median pit; the depression is situated considerably in front of 

 the mandibles. In S. gibba Nobili the median carina is flattened 

 and much widened a little behind the middle and has there a 

 small, a little oblong, convex area surrounded by a rather deeply 

 depressed ring, and placed a little in front of the mandibles. 



Lysiosquilla. In a rather large specimen of L. eusebia 

 Risso a very small and feeble depression a little in front of the 

 middle of the carapace above the mandibles; in another rather 

 large specimen and in small specimens nothing could be observed. 



In L. maculata F. no vestige was found. 



Pseudosquilla ciliata F. In two specimens a nearly circular, 

 very conspicuous and somewhat deep depression with two or 

 three tiny pits on the flat or a little convex bottom, situated a 

 little in front of the middle of the carapace and somewhat in 

 front of the mandibles. In a third specimen the depression is 

 small and shallow, in a fourth quite rudimentary. 



Odontodactylus scyllarus L. Slightly behind the middle of 

 the carapace a rather large, moderately shallow depres- 

 sion, in the middle of which a small, circular, somewhat convex 

 area. 



Gonodactylus Oerstedii H. J. H. A deeper or more shallow, 

 small, circular, depressed area a little behind the middle of the 

 carapace and above the mandibles. In young specimens the 

 depression is either considerably more feebly developed or not 

 discernible. 



