The "dorsal organ" in Crustacea Malacostraoa. 7Q 



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 5. 

 raphidea F. the organ is conspicuous and nearly as in 5. mantis. 



— In 5. Desmarcstii 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 5. 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. cusebia 

 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, 

 \-ery 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'. 



Odontodactylns 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. 



