354 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 39. 



The discovery of the true mouth-parts as well as the swimming 

 legs upon living specimens examined at Beaufort and Woods Hole 

 has completely changed the nature of the parasite and virtually makes 

 of it a new genus, but still retaining the old genus name. The case 

 is exactly similar to that of Echetus typicus described by Kroyer 

 as a Lernseid, but afterward found, when its head was discovered, 

 to belong to the Caliginse. 



ARTIFICIAL KEY TO THE SPECIES. 



a. Posterior portion of the fused thoracic trunk distinctly three-lobed; skin smooth, 



impressus Kroyer, 1837, p. 354. 



a. Posterior portion of fused thoracic trunk evenly rounded, with no trace of 



lobes b 



b. Fused thoracic trunk wider than long, overhanging and concealing in dorsal view 

 the genital segment and abdomen; skin smooth, .corpulenius, new species, p. 358. 



b. Fused thoracic trunk one-third longer than wide, genital segment and abdomen 

 wholly visible; skin covered with small warts. . .verrucosus, new species, p. 359. 



TUCCA IMPRESSUS Kroyer. 



Plates 48 and 49. 



Tucca impressus, Kroyer, 1837, p. 479, pi. 5, fig. 2, a to g. 



Female, — Body separated into three distinct regions, a cephalo- 

 thorax, a fused thorax, and a posterior portion consisting of the fifth 

 thorax segment, the genital segment and the abdomen. The cephalo- 

 thorax is a fusion of the head and the first thorax segment, and is small 

 and hemispherical in shape, being inflated dorsally and flattened 

 ventrally. 



The integument along each lateral margin is formed into a wide 

 lobed wing, made up of two layers of skin, dorsal and ventral, sepa- 

 rated from each other and supported upon a chitin framework 

 (fig. 112). 



The ventral layer is produced inward from the lateral margin toward 

 the mouth, and is separated a little from the ventral surface of the 

 head, leaving a narrow space between the two. In this space are 

 located the bases of the various mouth-parts, of the second antennae 

 and the first swimming legs. 



The thickened edge of the skin is about half way between the lateral 

 margin and the mouth, and forms an elliptical ring around the latter. 

 On the ventral surface of this raised edge appear anteriorly the first 

 antennae, and posteriorly the terminal joints of the first swimming 

 legs. 



The first antennae are four-jointed, the three basal joints about the 

 same width, the terminal one much narrower; every joint is heavily 

 armed with setae, which extend in a continuous row along the anterior 

 margin of the basal joint, and diagonall}^ across the ventral surface 

 of the second and third joints. The second antennae are three-jointed, 



