28 PROCEEDINGS OF THE NATIONAL MUSEUM VOL, 125 
platelike area of heavy sclerotization situated between and immediately 
posterior to these processes. 
Family EURYPHORIDAE 
Alebion gracilis Wilson 
FIGURE 13 
Alebion gracilis Wilson, 1905b, p. 128.—Lewis, 1966, p. 136, figs. 36-38. 
For synonymy, see Lewis (1966). 
Hosts AND DISTRIBUTION.—See Lewis (1966). 
Marerrtau.—4 males (USNM 120747) from the external surface of 
Carcharinus menisorrah (Miiller and Henle); 2 females (USNM 
120748) from the external surface of C. menisorrah. 
MEASUREMENTS (in mm).—2 females and 4 males: 
male 
female mean range 
6,6.55 3.62 3. 52-3. 81 
3.59 2.09 2. 04-2. 15 
3. OG 2. 12 1. 92-2, 22 
166) 046 0. 70-0. 81 
, 2.00 0.67 (all specimens) 
1 
0 
Total length, excluding caudal setae 6. 6 
Length of cephalothorax 3. 8 
Width of cephalothorax 2.8 
Length of genital segment 1.6 
Width of genital segment 9 
Length of genital segment processes eal 
Length of abdomen 0.7 
Length of egg strings (nonovigerous) 
Bis: 
.74 0. 56 0. 44-0. 67 
Description.—Male only (for description of female, see Lewis, 
1966). Male cephalothorax (fig. 13a) ovoid, consisting of cephalon 
and first 4 thoracic segments. Frontal region slightly less than one- 
tenth the total length of cephalothorax, with narrow membrane along 
anterior margin; division between frontal region and rest of cephalo- 
thorax distinct. Lateral margins of cephalothorax smoothly convex, 
bearing narrow membrane. Posterior lateral region with small, semi- 
lunar concavity, concavity with fine, hairlike process. Posterior median 
cephalothoracic region terminating at level of posterior lateral regions, 
posterior margin flatly concave medially, posterior surface bearing 
approximately 5 spinules laterally. Posterior sinus U-shaped, with 
frilled membrane and shelflike projection extending medially from 
outer surface, second membrane extending posteriorly from posterior 
outer surface. Dorsal surface with major grooves forming irregular 
H, anterior longitudinal legs of H terminating lateral to distinct 
ocular region. Median dorsal surface with 3 pairs of spines situated 
between ocular region and cross bar of H formed by major dorsal 
grooves. Free fourth pedigerous segment short, length approximately 
one-third the width, dorsal surface with small, platelike lateral ex- 
