16 BULLETIN 201, UNITED STATES NATIONAL MUSEUM 



dence. Ortmann examined specimens from three separate geograph- 

 ical regions, east coast of North American and Japan (1906), and 

 from Hawaii (1905). He referred all the specimens to L. typicus 

 but made careful notes of the differences and variations met with. 

 He paid special attention to three characters, the length of the ros- 

 trum, the number of teeth on the antenna! scale, and the number of 

 spines on the lateral margins of the telson, and he came to the con- 

 clusion that the variations met with in these characters was so wide 

 as to render them of little specific value. There are, however, two 

 other characters to which Ortmann, unfortunately, gave no atten- 

 tion, the tuberculation of the carapace and the shape of the antennal 

 scale. In the typical form of L. typicus the carapace is coarsely tuber- 

 culose, particularly in the anterior central region, and the antennal 

 scale is rotund, the breadth being about 0.7 to 0.75 of the total length. 

 In L. intermedins (Hansen, 1910) the tubercles of the carapace are 

 much finer and more numerous, and the antennal scale is longer and 

 narrower, about twice as long as broad, with the terminal spiniform 

 process straighter and longer than in L. typicus. In L. rotundatus 

 (Illig, 1930) the carapace is practically smooth and the antennal 

 scale has the shape and proportions of the type species. 



Using these additional characters it has seemed to me desirable to 

 separate the west Atlantic and Japanese forms as new species, and 

 the following key will serve as a guide to the known species of the 

 genus. 



KEY TO THE SPECIES OF LOPHOGASTER 



a 1 . Posterolateral angle of carapace rounded (carapace smooth, antennal scale 



of "rotundate" type) rotundatus 10 



a 2 . Posterolateral angle of carapace produced into a spine. 



6 1 . Antennal scale of broad "rotundate" type. 



c 1 . Carapace tuberculose typicus (p. 17) 



c 2 . Carapace microscopically spinulose americanus (p. 17) 



6 2 . Antennal scale of "elongate" type, about twice as long as broad, apical 



spine long and straight. 

 c 1 . Rostral spine longer than antennal peduncle. 



d 1 . Rostral spine very long, far outreaching antennal scale. 



spinosus (p. 21) 

 d 2 . Rostral spine shorter than antennal scale. 



e 1 . Carapace smooth; 6 to 9 teeth on antennal scale excluding terminal 

 spine; telson with 5 to 8 spines on lateral margins including long 



spines at apex longirostris (p. 21) 



e 2 . Carapace finely tubercular; 2 or 3 teeth on antennal scale; telson 

 with 4 spines on lateral margins, including terminal ones. 



intermedius P (p. 20) 



c 2 . Rostral spine equal in length to antennular peduncle; carapace coarsely 



granular; antennal scale with 2 or 3 teeth excluding terminal spine; 



telson with 4 spines including terminal ones japonicus (p. 19) 



10 Illig, 1930, pp. 405-407, figs. 7-10. 



