On Aquatic Carnivorous Coleoptera or Dytiscide. 713 
The simple course seems to be to use the name Cybister costalis, Aubé, for Aubé’s 
species ; this does not prevent those who are fond of archeological 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., Trogus 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. i 
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 Aubé’s C. 
L’herminieri from ©. giganteus. The smallest individual I have seen measures 
36 mm. by 20 m.m., the largest 41 m.m., by 23$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 differentiate the species at present. 
Brazil, Central America, Mexico, Guadeloupe, Antigua, Cuba. 1113. 
1118. Megadytes ducalis, n. sp.—Maximus, ovalis, convexus, nitidus, niger, 
capite 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. 474 m.m., lat. 
262 m.m., alt. 15 m.m. 
