REPORT ON THE CRUSTACEA MACRURA. 875 



synaphipod. Second pair of gnathopoda long, slender, and pediform. First pair of 

 pereiopoda chelate or subchelate and larger than the second, which is simple like the 

 others posterior to it. 



Oodeopus, n. gen. 



Carapace about one-fourth the length of the animal. Rostrum long and slender. 



Pereion narrow and subcylindrical. 



Five anterior somites of pleon subequal, the sixth longer than the preceding. 



Telson long, narrow, the terminal extremity fringed with hairs. 



Ophthalmopoda short ; ophthalmitis large, ovate. 



First pair of antennae biflagellate. 



Second pair of antennas furnished with an obtusely-pointed scaphocerite. 



Mandibles without synaphipod. 



The second pair of gnathopoda long, slender, pediform and six-jointed, and carrying 

 a basecphysis. 



First pair of pereiopoda large and chelate. Second pair robust, but more slender 

 than the first and simple. All the pereiopoda carry a basecphysis. 



Pleopoda biramose, posterior pair not longer than the telson. 



Observations. — The description of this genus is drawn from an immature animal, but 

 the one that is in the most advanced stage of development in the collection, and which 

 shows a tendency to develop the first pair of pereiopoda into a chela in the adult stage. 

 All the other specimens exhibit them in the simple form, which I take to be a still more 

 immature condition. 



It bears comparison with a young animal which Dana has figured under the name 

 of Rachitic/, spinalis, 1 which he captured in the Atlantic, off the harbour of Rio Janeiro, 

 on January 7, 1838. It, however, differs from this genus in having the rostrum short, 

 in the first pair of antennas having only a single fiagellum, and in the form of the 

 telson. It must, however, be the young of some closely allied genus, of which the one 

 taken as the type in this collection is in the most advanced condition, and exhibits 

 evidence of the relation it bears to an older form. 



Geographical Distribution. — Most of those found were taken in the Eastern Seas. 

 Four different forms that appear to represent separate species were procured off Cape 

 York, one off Cape Jackson, one off the New Hebrides, and one off Cape Verde in the 

 Atlantic. Dana took his specimen of Rachitia off the coast of Brazil. 



1 U.S. Explor. Exped., Crust., p. 667, pi. xliv. figs. 8o-&. 



