556 TRANSACTIONS OF THE 



an obsolete undulated branch proceeding obliquely towards the 

 tip ; beneath varied with blackish, piceous and yellow. 



Length one inch. 



A male of this species was taken by AVilliam Bennett in the 

 river beyond Vera Cruz, and, together with the two following, 

 presented to me by Mr. William Maclure. It is allied to the 

 D. marginaUs, F., but that species in form approaches the ovate; 

 the present also is much smaller and oval. [442] 



3. D. BiMARGiNATUS. — Black ; head and thorax rufous ; elytra 

 with a yellow vitta on the lateral submargin. 



Inhabits Louisiana. 



Body oval, blackish ; head honey-yellow, posteriorly black : 

 palpi and antennae yellowish ; thorax honey -yellow ) posterior 

 margin black, which is more dilated on the middle half; elytra 

 with three series of distant slight punctures; on the lateral sub- 

 margin a yellow vitta, which passes a short distance on the hu- 

 meral base, and posteriorly diverges a little from the margin, 

 attenuates, and does not reach the tip ; margin and epipleura 

 dull rufous, not reaching the tip ; beneath piceous-black ; pectus 

 and anterior feet yellowish ; terminal joints of the tarsi piceous ; 

 posterior pairs of feet piceous ; intermediate thighs dull yellow; 

 venter each side with obsolete piceous spots. 



Length less than half an inch. 



For this species I am indebted to the politeness of Mr. J. Bar- 

 abino, who sent it to me from New Orleans. 



[Afterwards described as Hydaticus fidvicoUis Aube. — Leg. 



COLYMBETES Clairv. 



1. C. TiENiOLis Say, (Dytiscus) Trans. Amer. Philos. Soc. — In 

 Mexico is a variety, being smaller. The specimen is a male, and 

 proves that the species must be placed in the present genus. It 

 was taken in the river beyond Vera Cruz. 



2. C. GUTTicoLLis. — Thorax yellowish with four black spots ; 

 head black, anteriorly and band of the vertex yellow. 



Inhabits Mexico. 



Head black ; a transverse yellowish band between the nearest 

 points of the eyes ; a dilated yellowish triangle occupying all the 

 anterior part of the head, the apex being at the middle of the 



[Vol. IV. 



