510 PROCEEDINGS OF THE NATIONAL, MUSEUM vol.88 



roughly rectangular in shape ; anal sinus deep, sides flaring on female 

 and in contact on male, lobes pointed with anal furcae simulating a 

 second more median tip to the lobes of the abdomen ; anterior end of 

 abdomen square. The whole effect of the animal is very flattened 

 and leaflike, flecked with brown. 



The lateral hook on the antennae is curved in an arc instead of 

 being more sharply bent; anterior hook curved as well as the spine 

 on the midventral surface of the hook. Spine at base of first antennae 

 small, those near midline of body larger, all sharp. Tip of first 

 antennae biramous, second antennae short. 



Suction cups small, edge supported by ribs composed of three or 

 four rods, with slight indications of others; about four triangular 

 lappets on the edge of the disk between the ribs (fig. 41, c) . Second 

 maxillae short and stout, basal plate with sharp teeth ; anterior pair 

 of postmaxillary spines very small, posterior pair hardly discernible 

 or lacking. 



Swimming appendages with flagella on the two anterior pairs. 

 Each of the first three pairs on the female with posterior ventral 

 ridges or lobes on the coxa progressively larger toward the third one. 

 Fourth appendage with a broadly rounded lamella on both the coxa 

 and basis. Tactile papillae fairly large. 



First swimming appendage of the male with a slight ridge across 

 the posterior ventral edge of the coxa. Second appendage with a 

 broad irregular lobe on posterior edge of coxa with distal edge longer. 

 On the dorsal side the posterior edge of the coxa is prolonged into a 

 machete-shaped flap directed toward the body over the base of the 

 third appendages (fig. 41, a). 



The third appendages have the precoxa somewhat enlarged; pos- 

 terior ventral edge of the coxa lobed, with the distal edge prolonged 

 laterally over the basis and the anterior distal edge prolonged as a 

 flap over it. The toe of the posterior lobe covers the broadened por- 

 tion of the basis, which contains the socket. There is a slight knob on 

 the distal anterior end of the endopod. 



There are two posterior lamellae on the fourth appendages similar 

 to those of the female. The peg is very stout but ends in a narrow 

 curved tip with a blade-shaped chitinous process under the tip. It is 

 surrounded with a chitinous ridge, as in other species. The smaller 

 rounded respiratory area fits into a concavity in the side of the semi- 

 lunar large one that extends to the second maxillae (fig. 41, h). 



The females have been reported to 19 mm. and the males to 12.5 mm. 

 A. Tnississippiensis is about as large as A. nobilis but very much more 

 flattened and expanded. The hosts are Lepisosteus osseus and Cylm- 

 drosteus platostomus from Fairport, Iowa. 



