112 



BRITISH FOSSIL CRUSTACEA. 



outer borders, which are more sharply pointed near the extremity. The form and proportion 



of the five distal joints agree very closely 

 with those in the palpus drawn on PI. XVII, 

 fig. 4 ; but the ischium and basos differ con- 

 siderably, and appear to be squeezed together. 

 The same squamate markings are seen on the 

 surface. (See Woodcut, fig. 32.) 



These mouth-appendages appear to be 

 much more robust than in Pterygotus, and 

 must have served, not only as powerful jaws, 

 but also to retain and bring within reach of 

 the mandibles the living or dead substances 

 to be devoured. 



Swimming -feet (Ectognaths) (PI. XVII, 

 figs. 1, 6, 6, and PI. XVIII, figs. 1, 6, 6). — 

 The largest swimming-foot of this species 

 with which I am acquainted is a detached 

 example in the British Museum. This spe- 

 cimen measures ten inches from the crest of 

 the maxilla to the terminal palette, the swim- 

 ming-foot itself measuring six inches in 

 length. The position and form of these organs 

 are well seen, in -situ, in PI. XVII, fig. 1, and 

 in the detached appendages figured on PL 

 XVIII, fig. 1. 



Coxa. — This joint in form may be roughly 

 compared to a right-angled triangle, the inner 

 or mandibular border and the base forming 

 the rectangle. The base measures 2-| inches 

 in breadth, to the outer angle of which the 

 great swimming-foot is seen to be attached, 

 the outer and longest side of the triangle mea- 

 suring 4-| inches; the upper end, which forms 

 the mandible, is contracted three inches from 

 Fig. 32.— Endognathary palpus of siimonia (natural size), u. the base, where it measures on! y ten lines 



Silurian, Lesmahagow, Lanarkshire. Original specimen _ •> 



in the Britisih Museum. in breadth ; the mandibular border is 1|- 



lines broad, and beset with 14 nearly equal-sized teeth one line in length. Some minute 

 squama? are observable upon the surface of this joint. 



Basos. — This is a small segment, four lines only in length, inserted at its proximal end 



