1887.] PROCEEDINGS OF UNITED STxVTES NATIONAL MUSEUM. 561 



erate and regular outward curve from side to side, broken in the center 

 by a relatively deep and narrow indentation, tbrongli which a large part 

 of the posterior ventral appendage is plainly visible from above. The 

 s])ecimen from which the general figure represented on Plate XXIX was 

 made, measures about 5.5""" in length of body, and this is the extreme, 

 length allbrded by our collection. The greatest width is about 2.5""". 

 Some specimens are proportionally wider, but only to a slight extent. 

 The egg-tubes are small, cylindrical, straight, and considerably longer 

 than the body. 



Variety Stimpsoni. — I was at first inclined to regard this variety as a 

 separate species, but as it agrees closely with the typical form in all the 

 ventral appendages, it does not seem to merit such distinction. The 

 body is proportionally wider than in both communis and dcntatus. The 

 cephalothorax is semi oval in outline, about one and one-half times 

 wider than long, and widest at the extreme posterior end, where the 

 lateral angles are produced in broad, rounded, wedge-shaped projec- 

 tions, which are shorter and more divergent than in dentatus, and larger 

 and broader tlian in communis. The lateral margins are moderately 

 convex and diverge rapidly backward from the frontal process, which is 

 narrower than in the typical form, gently convex on each side of the 

 slightly excavated middle portion, and more obliquely cut at the free 

 ends. The posterior margin is straignt between the projecting angles. 



The dorsal plates of the second body segment are widely separated, 

 very oblique, their laterally exposed margins very strongly rounded 

 and projecting far beyond the lateral margins cf the plates of the 

 fourth segment. The fifth segment is about one-fourth wider than long, 

 the width greatest near the middle and very little less than that of the 

 cephalothorax. Outer margin gently convex to near- the posterior an- 

 gles, where they form a veiy slight re-entering curve and terminate in 

 a stout, acute «piue on each side. The posterior margin is broadly in- 

 dented in the middle, on each side of which it is first strongly convex, 

 and then forms a deep re-entering curve, extending close np to the lat- 

 eral spines. Eutire length of the body 4.75"""; extreme width ]iearly 

 3""". The egg cases are similar to those of the typical form. 



Only alcoholic specimens of both of these forms have been seen by 

 the writer. The specimen of var. Sfimpsoni has been in alcohol for 

 many years and is of a very dark brown color, while all of those-of the 

 typical form are very light yellowish. The dorsal surface of the fiftli 

 segment is very slightly horny, wliile the upper plates of the four an- 

 terior segments are hard and rigid as in Fandarus. Viewed from the 

 ventral side, the dorsal plates of the second segment present features by 

 which this species may be distinguished from dentatus. In the typical 

 form, the outer margin of these plares extends far forward under the 

 cephalothorax, reaching quite to the reniforra processes of the second 

 maxilHpeds, and only the edge is exposed. In var, Stimpsoni it reaches 

 nearly as far forward, but a greater width is exposed, more as in den- 

 tatus. 



Proc. N. M. 87— —30 



