CONTRIBUTIONS TO MARINE BIONOMICS. 403 



was created for Mediterranean specimens, while Latreille's type came 

 from the west coast of France. 



2. Generic Characters. 



The genus Portumnus takes its place together with Carcinus, 

 Platyonichus, and Pohjhius in the Platyonichinre, a sub-family of the 

 Portunidu' distinguished from the Tortuninai by the absence of lateral 

 ridges on the pra^labial plate, and by the absence of a distinct accessory 

 lobe to the endopodite of the first maxillipeds. 



Portumnus is distinguished from Platyonichus by having the dactylus 

 of the fifth thoracic leg of a slender lanceolate form, and the carapace 

 not broader than long. In Platyonichus the dactylus is elliptical or 

 broadly oval, and the carapace is broader than long. To these dis- 

 tinctions I may add that in Platyonichus the interorbital margin is at 

 most tridentate or quadridentate, while in Portumnus the inner angle of 

 the orbit contributes a distinct accessory tooth to the frontal margin, 

 rendering this margin five-toothed, as in Polyhius Hensloicii. 



3. Specific Characters. 



The two species of the genus which alone are known to me are 

 P. latijics (Pennant) and P..nasutus. A description of the former 

 species may be found in Bell (1853) under the name Portumnus 

 variegatus. The characteristic features of P. nasutus are as follows : — 



Frontal area projecting in front of the orbits in the form of a 

 conspicuous triangular lobe with gently undulate lateral margins. 



The undulations mark the subdivision of the interorbital margin into 

 five rounded lol)ules, which correspond to the five interorbital teeth 

 of P. latijKS. The interorbital lobe bends downwards in front. 



The carapace is relatively broader than in P. Icdiiocs, so that the 

 antero-lateral margins make a sharper angle with the median transverse 

 axis. 



The orbit shows two superior fissures and one inferior fissure (imce 

 Latreille and H. Milne-Edwards, who mention only one superior 

 fissure), while in P. laiijKS the orbit is stated to be cither entire 

 (Bell; Leach, 1815) or provided with a single fissure above (H. Milne- 

 Edwards, 1834). 



The basal joint of the second antenna is movable. 



4. Colour. 



The colour of the carapace of Porttimmis 7iasutus is thus described by 

 Risso (181G, p. 31) — "yellowish-white, adorned with two great spots 

 of coral-red . . . The red spots are larger in the female than in the 



