8 U.S. NATIONAL MUSEUM BULLETIN 2 78 



24.(21) Ventral spine present between insertions of gnathopods 2. 



Caprella equilibra (p. 25) 



Ventral spine not present between insertions of gnathopods 2 .... 25 



25.(24) Propodus of gnathopod 2 with small spine on inner surface near poison 



tooth 26 



Propodus of gnathopod 2 without small spine on inner surface near 



poison tooth Caprella equilibra variant (p. 29) 



26.(25) Ratio of total length to length of basis of gnathopod 2 greater than 13.0; 

 dorsal surface of pereonites 1-4 usually spinose, cephalon with at least 1 



large spine Caprella septentrionalis (p. 44) 



Ratio of total length to length of basis of gnathopod 2 smaller than 13.0; 

 dorsal surface of pereonites 1-4 usually smooth, cephalon infrequently 

 with small spine Caprella linearis (p. 30) 



Aeginella Boeck, 1861 



Flagellimi of antenna 2 biarticulate, swimming setae absent; 

 mandibular palp 3-segmented, setal formula for terminal article 

 1-x-l, molar present; outer lobe of maxilliped larger than inner lobe; 

 gills on pereonites 3 and 4; pereopods 3 and 4 absent, pereopod 5, 

 6-segmented; abdomen of male and female with pair of appendages 

 and pair of lobes. 



Type-species: Aeginella spinosa Boeck, 1861 (by monotypy). 

 Remarks. — The genus Aeginella is very closely related to Aeginina 

 and Proaeginina, differing from them only by the structure of the 

 abdomen. There is a gradation from 1 pair of appendages with lobes, 

 2 pairs of appendages, to 2 pairs of appendages with lobes in the 

 series Aeginella-Proaeginina- Aeginina. 



Aeginella spinosa Boeck, 1861 



Figures 2, 3, 54 



Aeginella spinosa Boeck, 1861, pp. 673-674; 1871a, pp. 272 (192)-273 (193); 

 1873-76, pp. 684-686, pi. 32, fig. 4.— M. Sars, 1863, pp. 290-291.— Mayer, 

 1882, p. 36; 1890, pp. 36-37, pi. 1, fig. 24, pi. 5, figs. 30-33; 1903, p. 61.— 

 G. Sars, 1886, pp. 70, 89; 1895, pp. 653-654, pi. 235, fig. 1.— Norman, 1886, 

 p. 26; 1905a, p. 26.— Hansen, 1887b, pp. 172-173; 1895, p. 130.— 

 Vanhoffen, 1897, p. 213.— Nordgaard, 1905, p. 185.— Stephensen, 1913a, 

 pp. 222-223; 1916, p. 295; 1929a, p. 178, fig. 332; 1929b, pp. 19, 34; 1933, 

 pp. 60, 77; 1935, p. 118; 1940, p. 69; 1942, pp. 429-430, 502, 503; 1944a, 

 pp. 48-49, map 9; 1944b, pp. 135-136, 148, 159, 162.— Derjugm, 1915, pp. 

 453, 456.— Schneider, 1924 (1926), p. 59.— McCain, 1966, p. 92. 



Diagnosis. — Since this genus is monotypic, the characters of the 

 genus are diagnostic for the species. 



Description. — Body rather robust, spinose; cephalon mth anterior 

 projection, separated from pereonite 1 by distinct suture. Pereonite 

 1 with dorsal anterior spine. Dorsal sm'face of pereonite 2 with pair 

 of spines at midlength of pereonite and single posterior spine, inser- 

 tion of gnathopod 2 with small spine, anterolateral margin produced 



