On Aquatic Carnivorous Coleoplem or DytiscidcB. 713 



The simple course seems to be to use the name Cybister costalis, Aube, for Aube's 

 species ; this does not prevent those who are fond of archaeological nomenclature 

 citing "? Dytiscus costalis, Fab.," in addition if they desire so to do. 



South America, (Cayenne, Guyana, Demerara) {? Antilles ? United States of North America). 1112. 



Group 6. 



1117. Cybister giganteus. Cast., Tragus giganteus, M.C. — Major, ovalis, sat 

 convexus, nitidus, nigricans, capite anterius prothoraceque lateribus testaceis, elytris 

 vitta intramarginali posterius obsoletescente testacea ; pedibus quatuor anterioribus 

 piceo-rufis. femoribus versus basin magis nigricantibus ; posterioribus fere nigris 

 Long. 41, lat. 23 m.m. 



In the male the anterior tarsi are small, (for the size of the species) attaining 

 from 2| to 3 m.m. in the transverse direction, their claws are short ; beneath the 

 palettes are narrow, the pubescent area is large, and the basal fringing hairs are very 

 little developed ; on the middle feet there is a narrow line of sexual pubescence on 

 the under side of the basal joint, and the claws are short. The female has no trace 

 of sexual sculpture. 



This species varies much in size and form, and also in the width of the marginal 

 yellow band on the elytra, as well in the distinctness of its development near its 

 termination. 



I have not been able to find any means of distinguishing the variations 

 with certainty, and cannot point out any character for separating Aube's C. 

 L'herminieri from C. oriaranteus. The smallest individual I have seen measures 

 36 m.m. by 20 m.m., the largest 41 m.m., by 23l m.m. I have examined the 

 cedeagus, in all the males I have seen, and find slight variations in its form, but 

 no difference of importance in this respect between the Brazilian C. giganteus and the 



C. L'herminieri from Guadeloupe. This organ in this species remains largely in a 

 membranous condition, and does not exhibit the fine and perfect structure seen in 



D. limbatus (No. 1157), and its allies. Two individuals from Brazil, however, 

 show so much difference in the form of the lower portion of the cedeagus as to render 

 it probable they will form a distinct species ; but as I can see no other character 

 to distinguish them from certain varieties of C. giganteus, I do not think it proper 

 to attempt to dift'erentiate the species at present. 



Brazil, Central America, Mexico, Guadeloupe, Antigua, Cuba. 1113. 



1118. Megadytes ducalis, n. sp. — Maximus, ovalis, convexus, nitidus, niger, 

 €apite anterius prothoraceque ad latera testaceis, elytris vitta intramarginali ante 

 apicem evanescente testacea, pedibus quatuor anterioribus piceo-rufis, femoribus 

 versus basin nigricantibus, pedibus posterioribus nigris. Long. 471 m.m., lat. 

 265 m.m., alt. 15§ m.m. 



