American Species of Palicus. 95 



C. Lateral teeth 4 besides the orbital. fragilis Rathbun. 



C / . Lateral teeth less than 4 besides the orbital. 

 D. Median suborbital lobe midway between the outer and inner 

 lobes. 



cursor A. Milne Edwards = dilatata A. Milne Edwards. 



D'. Median suborbital lobe much nearer the outer than the inner 



lobe. gracilis Smith. 



Palicus alternatus Rathbun, new species. 



Carapace subquadrate, coarsely granulate. Front with four distinct 

 lobes, the median pair smaller and more deeply separated from each other 

 than from the outer pair. Superior orbital lobes subquadrate. Outer 

 margin of outer orbital tooth nearly straight. Median lobe of inferior 

 margin most advanced at its inner angle. Lateral teeth two, broad, 

 lobate, obtuse. In large specimens a third very small tooth or tubercle 

 behind the second. 



There are two forms of the male in this species. In one the appendages 

 of the first segment of the abdomen are strong and twisted, the tip. is 

 bilobed, the inner lobe thinner and longer than the outer. In the second 

 form the appendages are weaker and not twisted, the tip less spreading. 



In the first form the chelipeds are very unequal, the left is always 

 slender and weak, the right large and heavy. Both chelipeds are tuber- 

 culate and pubescent. The carpus is covered with irregular laminiform 

 lobes ; the manus is surmounted by a double crest of the same. The 

 width of the right manus at its distal end equals one-half the length of 

 the carapace. Pollex very short. Dactylus strongly bent down, over 

 lapping the pollex at the tip. Left manus a little more than one-third 

 the width of the right, enlarging but little towards the long and rather 

 narrow fingers. 



In the second form of the male the right manus is about twice the width 

 of the left and its fingers are also long and slender. In the females the 

 chelipeds are more nearly equal. 



The second ambulatory leg is about twice the length of the carapace ; 

 the first reaches about the middle of the propodus of the second ; the third 

 reaches about the middle of the dactylus of the second. The meri are 

 rough with squamose tubercles, and have two longitudinal grooves on the 

 upper surface and one on the anterior surface. The anterior margin ter 

 minates in a blunt rectangular tooth in the second and third pairs ; in the 

 first pair this tooth is produced outward toward the carpus. Posterior 

 margin of the dactyli concave as a whole, but nearly straight for the 

 proximal two-thirds. 



The two forms of the male agree in every respect excepting in the 

 chelipeds and abdominal appendages. These forms perhaps represent 

 alternating conditions in the life of an individual similar to those exist 

 ing in the genus Cambarus; the first form that which occurs during the 

 breeding season, the second that which occurs between breeding seasons. 

 No other species of the genus exhibit this phenomenon, a fact which may 



