417 



legs, though otherwise exhibiting a general relationship to the 3 preceding 

 genera. In addition to the typical species described below, the form recorded 

 by Th. Scott as Mesochra spinicauda is evidently referable to the present genus. 



Leptastacus macronyx, Scott 



(Suppl. PL 40). 



Tetragoniceps maeronyx, Th. Scott, Additions to the Fauna of the Firth of Forth. 10th Ann. 

 Eep. of the Fishery Board for Scotland, Part. IV, p. 253, PI. X. figs. 1928. 



Specific Characters. Female. Body slender and narrow, sub-linear in 

 form. Cephalic segment of moderate size and rather deep; rostrum comparatively 

 short and obtuse at the tip. Urosome about the length of the anterior division 

 and slightly attenuated behind, genital segment of moderate size and not sub- 

 divided, last segment smaller than the preceding one. Caudal rami considerably 

 longer than the anal segment and somewhat divergent, tapering slightly distally, 

 outer edge armed close to the end with a slender spine tipped with a thin bristle, 

 apical setae very unequal, the inner medial one much the strongest and having 

 the proximal part thickened, spiniform; dorsal seta issuing close to the end of 

 the ramus. Anterior antennae very slender, equalling in length the 3 first seg- 

 ments combined, and composed of 7 joints, the first 3 nearly of equal length, 

 the 4th much smaller, terminal part about Va as l n g as tne proximal. 

 Posterior antennae with the distal joint scarcely dilated at the end and having 

 the apical setae comparatively short, outer ramus represented only by a small 

 knob-like prominence tipped with a delicate bristle. Mandibular palp distinctly 

 biarticulate. Posterior maxillipeds of quite unusual size, propodos somewhat fusi- 

 form in shape and perfectly smooth, dactylus exceedingly slender and somewhat 

 flexuous, being clothed in the outer part with thin spinules, accompanying bristle about 

 half the length of the dactylus. 1st pair of legs with the inner ramus only slightly 

 longer than the outer, its proximal joint slightly dilated and carrying inside, a 

 little in front of the middle, a slender seta, distal joint narrow linear and ex- 

 ceeding half the length of the proximal one, apical spine and seta very slender. 

 The 2 succeeding pairs of legs of essentially equal structure, both rami very slender, 

 the inner one the shorter and having its 2 joints of about equal length, tip armed 

 with only a single spine accompanied outside by a small dentiform projection. 

 4th pair of legs with the outer ramus much elongated, being fully twice as long 

 as the inner, middle joint the largest and provided inside near the base with 

 a well-developed seta, terminal joint carrying inside 2 rather strong setae 

 and at the tip 3 unequal spines. Last pair of legs without the slightest trace 

 of a distal joint, each forming a somewhat triangular piece, produced outside at 



