60 HYDROPHILIDA. 
In the male the mentum and the lateral portions of the submentum are quite dull, 
owing to a very dense, fine, rugulose punctuation, while in the female these parts are 
shining and rather finely and moderately closely punctate. 
15. Tropisternus lateralis. 
Hydrophilus lateralis, Fabr. Syst. Ent. p. 228°. 
Tropisternus lateralis, Cast. Hist. Nat. ii. p. 53°; Lec. Proc. Ac. Phil. 1855, p. 367 °. 
Hydrophilus nimbatus, Say, Journ. Ac. Phil. i. p. 203 *. 
Hab. Nortu America 4, from New York southwards.—MeExico, Jalapa, Oaxaca (Hége), 
Parada, Guanajuato (Sadlé) ; Guatemaa, Duefias, San Gerénimo, Cubilguitz (Champion), 
Guatemala city 5000 feet (Salvin, Champion).—ANTILLES, Cuba, Antigua; SouTH 
AMERICA ! 2, to Monte Video. 
This species is very variable ; and I am by no means certain that it does not consist 
of several very similar and rather variable species; but as, after several days devoted to 
examination of specimens from various localities, Iam unable to arrange them as separate 
Species in a satisfactory manner, 1 am obliged at present to treat all the forms as one 
species. The variations in Mexico and Central America affect the size, colour, form, and 
sculpture, and the existence or absence of a marked ventral spine at the extremity of 
the hind body. The colour of the upper surface varies from a very dark obscure fuscous 
brassy colour to a brilliant brassy green; the yellow cincture is sometimes very broad ; 
and in such case the individuals approach very closely indeed to the Californian 
T. limbalis, Lec. ; at other times it is very narrow. In many of the darker individuals 
there is a pair of lines of large punctures near the margin of the wing-cases, and others 
near the suture. The last ventral segment shows a prominence at the extremity, which is 
sometimes so slight as to be readily overlooked, while in others it forms on the apical part 
of the segment an abruptly elevated fold, the extremity of which projects, to a greater or 
less extent, asa short free spine ; this latter is not a sexual character: but it is subject to 
a slight amount of variation according to sex; for although males may be found without 
the carina, and females with the carina strongly developed, yet if specimens from the 
same locality, quite agreeing in other respects, be selected and examined, it is found 
that the males have the carina and spine on the whole more conspicuous than it is in 
the females. 
16. Tropisternus obscurus. (Tab. II. fig. 7.) 
Brevior, convexus, posterius attenuatus, niger, subeanescens, pedibus piceis; subtilius punctulatus ; pedibus 
posterioribus crassiusculis, femoribus area pubescente parva, tibiis ciliatis ; spina sternali elongata, acumi- 
nata, levigata; margine pleurali omnino impunctato; abdominis apice subtuberculato, nullomodo 
carinato. 
Long. 5, lat. 27 lin. 
Hab. GUATEMALA, Duefias (Champion). 
