246 The University Science Bulletin. 



small, rounded, fairly regular in size, shape and spacing; bear a few small 

 secondary teeth on caudal edge ; margin of valve between teeth is also notched 

 with, small secondary teeth; tip notched with small teeth on both dorsal and 

 ventral edges, not continuous around the tip, nine present on ventral edge; 

 area of ducts conspicuous, granular in appearance, circular duct openings vis- 

 ible; open along ventral apical edge, at extreme apex, along dorsal edge of 

 toothed area, and irregularly in the basal area where elongate ducts are vis- 

 ible; the two valves of the pair are joined one to the other by an elongate, 

 distinct, heavily chitinized connection present on the dorsal edge about a third 

 of the length. 



Deltocephalus inimicus (Say). 



(PI. XXIII, fig. 8; pi. XXX, fig. 8.) 



Length, 1.1 mm.; greatest width, 0.11 mm. About the same width for en- 

 tire length, narrows caudad to apex, preapical prominence wanting; slightly 

 curved; tip greatly narrowed, extreme apex rounded, chitinization moderately 

 heavy; strengthening rod extends caudad "as far as last dorsal primary tooth. 

 Toothed area on dorsal edge occupies apical half; primary teeth thirteen in 

 number, small, rounded, rather regular as to size, shape and spacing; bear a 

 few small secondary teeth on caudal edge; margin of valve between primary 

 teeth is also notched with small teeth; ventral edge of tip is notched with 

 small teeth, dorsal edge devoid of teeth at apex, fifteen present on ventral 

 edge; area of ducts somewhat granular, though elongate ducts are present, 

 circular duct openings visible; open along ventral apical edge, at extreme 

 apex, along dorsal edge of toothed area and irregularly in the basal region ; the 

 two valves of the pair are joined one to the other by an elongate, distinct, 

 heavily chitinized connection present on the dorsal edge at about one-third 

 the length. 



Deltocephalus jlavicosta Stal. 



(PI. XXIII, fig. 9; pi. XXX, fig. 9.) 



Length, 1 mm.; greatest width, 0.1 mm. Apical portion bearing teeth 

 occupies a little more than one-half the length, is slightly wider than the 

 basal portion, narrows caudad to apex; no preapical prominence; slightly 

 curved, tip narrowed, extreme apex bluntly rounded, chitinization moderately 

 heavy; strengthening rod extends caudad as far as last primary tooth. 

 Toothed area on dorsal edge occupies a little more than the apical half; 

 teeth twelve to thirteen in number, small, rounded, rather regular in size, 

 shape and spacing; bear a few small secondary teeth along the caudal edge; 

 margin of valve between primary teeth is also notched with small secondary 

 teeth; tip notched with small teeth on ventral edge, dorsal edge devoid of 

 teeth at apex, eleven present on ventral edge; area of ducts somewhat granu- 

 lar in appearance, though elongate ducts are visible; open along ventral apical 

 edge, at extreme apex, along dorsal edge of toothed area, and irregularly in 

 the basal area; the two valves of the pair are joined one to the other by an 

 elongate, curved, heavily chitinized connection present on the dorsal edge at 

 about one-fourth the length. 



