ISOPODS OF NORTH AMERICA. 157 



27. Genus ALCIRONA Hansen. 



Peduncle of the first pair of antennae composed of two articles. 



First maxillae with the apex of the third article furnished with two 

 spines. Second maxillae simple, laciniae not distinct. 



Mandibles becoming narrower from the base to the apex; movable 

 lacinia very small or wanting, molar part absent. 



Clypeus very large, long, and very wide, semilunar in shape, with 

 the post-lateral angle reaching beyond the middle of the mandibles 

 and almost to the articulation of the mandibular palp. 



ANALYTICAL KEY TO THE SPECIES OF THE GENUS ALCIRONA. 



a. First pair of antennae, with flagellum of seventeen articles, extend to the end of 

 the fifth article of the peduncle of the second pair of antennae. Second pair of 

 antennae, with flagellum of thirty-five articles, extend to the posterior margin 

 of the seventh thoracic segment. The first article of the peduncle of the second 

 antennae is twice as long as the second; the third is as long as the first; the 

 fourth is twice as long as the third; the fifth is twice as long as the fourth. 

 Last three segments of thorax with rows of stiff hairs on the posterior margin, 

 and all the segments of the abdomen and the uropoda are covered with short 

 stiff hairs Alcirona krebsii Hansen 



a'. First pair of antennae, with flagellum of seven articles, extend to the end of the 

 fourth article of the peduncle of the second pair of antennae. Second pair of 

 antennae, with flagellum of seventeen articles, extend to the middle of the 

 third thoracic segment. The first three articles of the peduncle of the first pair 

 of antennae are short, the fourth and fifth articles subequal and each about 

 twice as long as the third article. Last five segments of thorax with rows 

 of stiff hairs, and all the segments of the abdomen and the uropoda covered 

 with short stiff hairs Alcirona hirsuta Moore 



ALCIRONA KREBSII Hansen. 



Alcirona krebsii HANSEX, Vidensk. Selsk. Skr. (6), V, 1890, pp. 391-392, pi. vm, 

 figs. 1-lq. RICHARDSON, Proc. U. S. Nat. Mus., XXIII, 1901, p. 519; Trans. 

 Conn. Acad. Sci., XI, 1902, p. 290. 



localities. Off Cape Catoche, Yucatan; St. Thomas, West Indies; 

 Castle Harbor, Bermudas, in the cavities of living bathing sponges 

 and in dead coral. Two specimens were taken from the tins of a Ham- 

 let Grouper. 



Depth. 25-28 fathoms. 



Body oblong-ovate, a little more than twice as long as wide, 5 mm.: 

 11 mm. Head wider than long, 1 mm. : 2 mm. , with the anterior margin 

 rounded. Eyes small, round, composite, and situated in the antero- 

 lateral angles of the head. The first pair of antennae have the first 

 article long; the second is fused with the first; the third is longer than 

 the first. The flagellum is composed of eighteen articles. The first 

 antennae extend almost to the end of the fifth article of the peduncle of 

 the second antennae. The second pair of antennae have the first article 



