3C ) 

 S. I. Smith — Early Stages of the American LolMer. 261 



branchial appendages are exactly like the corresponding parts of the 

 second and third pairs of legs. 



In the posterior pair of legs (plate XVII, fig. 6, terminal portion of 

 one, enlarged 40 diameters) the endopodus is slightly more slender 

 than in the fourtli pair, the propodns is proportionally a little lon- 

 ger, and the slender stylet at the tip of the dactylus is considerably 

 more than twice as long as the dactylus itself. The exopodus is like 

 that of the other legs, and the single rudimentary, branchial appen- 

 dage is of the same size as those of the other legs. 



The abdomen is slightly longer than the entire length of the cara- 

 pax, quite slender, tapers gradually toward the extremity, and all 

 the segments except the expanded telson are nearly cylindrical. The 

 first segment does not extend beyond the posterior margin of the 

 sides of the carapax and is entirely unarmed. The second, third, 

 fourth and fifth segments are subeqiial in length, and each is armed 

 with a stout dorsal spine arising from the posterior margin and curved 

 backward, and has the posterior margin produced each side below 

 into a smaller, straight, tooth-like spine. The lateral spines increase 

 slightly in size from the second to the fifth segment. The dorsal 

 spine U2)on the second segment is shorter than the segment itself, that 

 upon the third is longer than the segment, and those upon the third 

 and fourth are still longer and nearly equal. (Plate XVIIl, fig. 8, 

 lateral view of the fourth segment, enlarged 20 diameters, and fig. 9, 

 diagram of a section of the same segment seen from behind, enlarged 

 30 diameters.) The penultimate segment is a little longer than the 

 preceding, and is armed above with two short spines like the one upon 

 the second segment, except that they are more curved toward the ex- 

 tremities. 



The telson (plate XVIII, fig. 1, enlarged 20 diameters, and la, 

 portion of one of the angles, enlarged 40 diameters) is closely arti- 

 culated to the penultimate segment, so as apparently to admit of no 

 motion between them, and is developed into a very large lamellar 

 swimming appendage somewhat triangular in outline, with the pos- 

 terior margin deeply concave. This caulal lamella is fully as long as 

 the four ]jreceding segments together and nearly the same in breadth 

 across the posterior angles, being fully as broad as the widest part of 

 the carapax. The posterior margin is deeply and regularly concave 

 in outline, is armed with a stout median spine and the latei*al angles 

 project in long spiniform processes, while each side between the 

 lateral angles and the median spine there are fourteen or fifteen stout 

 plumose seta3 articulated to the margin (plate XVIII, fig. la), the seta 

 next the lateral angle being very much smaller than the others. 



