REPORT ON THE CRUSTACEA MACRURA. 271 



extremity of the ophthalmopod ; on the outer side is a short stylocerite, and at the distal 

 extremity of the first joint, which is subequal in length to the rostrum, is a short, sharp 

 tooth; the second joint is nearly as long as the first, and furred with short hairs; the 

 third is short and smooth, carrying at its extremity two flagella, of which the inner and 

 lower is the more robust; they are subequal in length, nearly as long as the peduncle, 

 and with it longer than the carapace. 



The second pair of antennae has the basal joint of the peduncle robust and the 

 terminal slender, it carries a scaphocerite that is subequal in length to the peduncle of 

 the first pair, and is very rigid on the outer surface, and terminates in a subapical tooth. 

 The flagellum is slender, very flexible, and once and a half as long as the entire animal. 



The mandible carries a synaphipod that has the first joint large and broad, the second 

 narrow and short, and both roughly pilose. 



The second pair of gnathopoda is slender, reaches as far as the distal extremity of 

 the rostrum, and carries a basecphysis that extends as far as the distal extremity of the 

 carpos. 



The pereiopoda are slender, the third pair being the most slender, and longer than 

 the preceding, and terminating in a slender chela. The fourth pair is more slender 

 and slightly longer than the third, and terminates in a styliform dactylos that is nearly 

 as long as the propodos. The fifth pair is lost. 



The first pair of pleopoda is single-branched, the others are biramose. The sixth 

 pair forms the lateral plates of the rhipidura, and the outer is nearly twice as long as the 

 telson ; it has a diaeresis near the middle, and on the outer distal angle a small tooth. 



The ventral surface of the pereion is smooth at the posterior extremity, continuing 

 forwards to nearly the penultimate pair of pereiopoda, and is further advanced on each 

 side than in the middle, from which point the stalk of a spade-shaped plate projects, and 

 covers the ventral space between, and overlaps the coxae of the fourth pair of pereiopoda. 



Observation. — This species bears a close resemblance to the imperfect specimen described 

 and fioured by Dana, under the name of Penaeus tenuis, taken from the stomach of a fish, 

 caught in the Atlantic, off the coast of North Patagonia, excepting that instead of seven 

 teeth on the rostrum, Dana's species has nine or more. " The beak is broken, and we cannot 

 give the character of the under margin or extremity." 1 "Length one and a half inch." 



Penseus gracilis, Dana. 



Penxus gracilis, Dana, U.S. Explor. Exped. Crust., p. 606, pi. iv. fig. 7, a, l>. 



Slender ; carapace about one-third the length of the pleon, rostrum dorsally armed 

 with four or five small teeth, of which two are posterior to the frontal margin, and 

 a third is on the gastric region. The lower margin of the rostrum is smooth. Anterior 



1 Dana, torn, cit., p. 605, pi. xl. fig. 6. 



