21 



1. PoTAMON (Potamon) fluviatile (Latreille), var. ibericum 

 (Marschall de Bieberstein). - (Fig. 37.) 



Cancer iberious, Marschall de Bieberstein, Mem. Soc. Imp. Moscow, II., 1809, p. 4, pi. i., fig. 1. 

 Potamon {Potamon) ibericus, Mary J. Rathbiin, Nouv. Archiv. du Museum, Paris (4), VI., 1904, p. 25fl, pi. 

 ix. , fig, 4 {ubi synon.). 



Carapace length, in large adults, about l?,ths its greatest breadth ; depth 

 about two-fifths its length ; moderately convex fore and aft, less so from side to 

 side. Gastric region well defined, except postero-laterally, the epigastric and 

 mesogastric areolae distinct anteriorly, but other areolation quite indistinct. 

 Cardiac region distinguishable but not well demarcated. Branchial regions not 

 distinctly areolated. t!ervical groove fairly but not equally distinct in all its 

 course, cutting the post-orbital crests at a point in Hne with the inner angle of 

 the external orbital spine. The greater part of the dorsum of the carapace is 

 smooth, but the frontal and the anterior limit of the gastric region are rugose, 

 and the antei-o-lateral surface of the epibranchial regions is obliquely rippled. 

 The sidewalls of the carapace are obliquely rippled, and the pterygostomian 

 regions and the well-defined suborbital lobes are pimpled. The antero-lateral 

 margins of the carapace, which are longer than the ill-defined postero-lateral 

 margins, are clean cut, gently curved, raised, and elegantly crenulate, the 

 denticles regularly decreasing in size from the subacute epibranchial tooth 

 backwards. 



Front moderately declivous, very distinctly bilobed, its breadth in the 

 adult slightly over one-third the greatest breadth of the carapace, its edges 

 clean cut, somewhat everted, and usually smooth. Orbital margin also clean 

 cut and somewhat everted : external orbital tooth prominent, subacute, 

 separated from the lower border of the orbit by a notch. 



Epigastric crests tumid, rugulose ; separated fi-om, overlapping, and well 

 in advance of the post-orbital crests ; the latter have a thin, almost sharp, edge, 

 except for the small ragged outlying lobule cut off' by the cervical groove. 



In the abdomen of the adult male the length of the 6th segment is more 

 than a half but less than two-thirds its greatest breadth, and that of the 7th is 

 a little less than its greatest breadth. 



Autennular fossse narrow ; interantennular septum very broad, formed in 

 about equal parts by a process of the epistome and an infolded thickening of 

 the front. 



1st (true 2nd) antennal joint about as broad as long; 2nd and 3rd (true 

 3rd and 4th) joints in contact with and covered by the front. 



Mandible with a high sharp incisor edge, and a narrow obliquely-ti'uncated 

 molar facet : palp of the ordinary form, i.e., the terminal joint not bilobed. 



All three pairs of maxillipeds have long exopodites with well-developed 

 flagella. The 2nd joint of the endopodite of the first paii* is a broad obtri- 



