24 Bulletin Vanderbilt Marine Museum, Vol. V 



The sixth segment has a distinct, large V-shaped groove, the outer 

 side of which defines the inner margin of the thickened lateral border, 

 the base of the V being near and subparallel to the posterior margin, 

 while the inner side of the V runs forward and widens outwardly 

 uniting with a short transverse groove that runs inward subparallel 

 to the anterior margin of the segment. 



The telson is almost twice as wide as long, with the outer margins 

 widely rounded and, in very large adults, rather bluntly truncated 

 distally and having a small faint median notch. There is a very dis- 

 tinctly defined median dorsal elevation, in the form of an elongate 

 triangulate tooth, arising at the base of the telson and terminating 

 subdistally, the lateral margins beginning to converge about at a point 

 one-third of its length from the base, and being emphasized from this 

 point to the apex by a distinct groove. On the median region of the 

 ventral surface of the telson there is a similar, but smaller and not 

 quite so elevated a triangulation. The proximal margin of the telson 

 is emphasized by a thickened, transverse carina, and immediately 

 below it is a distinct groove on the outer side that runs almost to the 

 median line, vanishing on either side of the base of the median tri- 

 angulation. The lateral margin is thickened, terminating in a sharp 

 distal spine; a groove parallels the thickened lateral margin, in very 

 young specimens and those up to about three and one half inches 

 length, so far as observed, this carina extends almost to the distal 

 tooth, but in the three large specimens, 6 to 8 inches long, this carina 

 and groove vanish about midway the length of the segment. On 

 either side of the median dorsal tooth there is a longitudinal bar that 

 extends the length of the segment and terminates distally, bluntly. 

 Outside of this, on either side, there is an oval part, which in young 

 specimens, three to three and one-half inches long, is covered with 

 low, blunt granules. On the very large adults these granules have 

 entirely disappeared and are replaced by coarse punctae. There 

 coarse pits also occur abundantly on the median lateral and outer 

 lateral regions. 



In the largest specimen a second spine occurs, on the distal margin, 

 about one-third the distance between the first spine and the median 

 notch. In the very large specimens, the median distal margin, inside 

 this the second spine is blunt, thickened, with a slight but definite 

 node, about two-fifths of the distance between the second tooth and 

 median notch, which node represents what in the younger adults is 

 two definite teeth closely related to each other. In these young sped- 



