40 Bulletin, Vanderhilt Marine Museum, Vol. II 



third thoracic segment is short and has the lateral part prominently 

 produced, narrowed, curved, acute and forward and downward point- 

 ing tooth ; below which on the ventral surface there is another acute, 

 forward directed spine. The fourth thoracic segment is one and one- 

 half times as long as the third and is considerably longer on the lateral 

 region than is the preceding segment; the lateral margin is cut into 

 a smaller triangle at the anterior angle and a longer unequal-sided 

 triangle at the posterior angle. The fifth and sixth thoracic segments 

 are each equal in length to the fourth, but the lateral margin of the 

 fifth segment is nearly right-angled anteriorly, separated by a very 

 shallow sulcus from the broad triangular area of the posterior angle ; 

 the lateral margin of the sixth thoracic segment is nearly right-angled, 

 a little convex on its anterior margin and slightly concave on the lat- 

 eral margin ; the posterior portion of the lateral margin is brief and 

 is concealed by the rounded overlapping flap ; the first five abdominal 

 segments are subequal in length; the sixth segment is about a milli- 

 meter shorter and about 1.5 mm. narrower on each side. With the 

 exception of the rounded, anteriorly projecting flap of the first abdom- 

 inal segment, the lateral parts of the six abdominal segments are sim- 

 ilar ; the margin relatively straight and thickened, terminating at the 

 posterior angle of each segment in an acute tooth. There are eight 

 longitudinal carinae, extending the length of the six abdominal seg- 

 ments. The innermost or submedian pair of these carinae also extends 

 the length of the four visible thoracic segments, as does also the upper 

 lateral pair of carinae. The lower lateral pair of carinae terminate on 

 the flap-like projection of the first abdominal segment; the outermost 

 or marginal pair of carinae lose their continuity anteriorly on this 

 same segment. On the third to sixth abdominal segments each carina 

 terminates posteriorly in a small tooth, those of the third segment 

 being quite weak (possibly absent in some instances) while those of 

 the sixth segment are more emphasized than any of the others. 



The telson is about one millimeter wider than long, with a pro- 

 nounced median keel that ends subdistally in a blunt tooth in old male 

 specimens, or an acute tooth in young adults, below which there is a 

 blunt node between the two submedian elevations which terminate 

 distally in an acute, primary tooth. Between these there are secondary 

 teeth, the number varying from five to seven, on each side of the 

 median notch. In young specimens these secondary teeth are quite 

 bluntly triangulate ; in older specimens they are even more rounded. 

 Between the submedian primary teeth and next, or lateral pair of 



