78 HYDROPHILIDA. 
8-jointed, whereas in Derallus there are but seven joints. In other respects, however, 
the two genera are closely allied. The genus Volvulus has latterly been merged in 
Berosus; but such a proceeding is a very erroneous one, the two genera being far from 
closely allied. In regard to the abdominal structure the three genera under conside- 
ration form an interesting series. In Berosus there are five external segments, and 
a sixth, but still horny, retracted segment. In Derallus there are likewise five external 
segments, but the sixth retracted horny segment has disappeared; while in Volvulus 
there are but four external segments, and a fifth retracted horny segment; this fifth 
segment, although retracted, is notched in a similar manner to what it is in Deratlus 
and Berosus, where it remains external. The whole border or hind margin of the 
fourth segment in Volvulus is set with short horny teeth (which may possibly be a 
portion of a stridulating-apparatus). In Beresus the hind margin of the fifth segment 
is densely set with similar though smaller teeth; but in Derallus they appear to be 
absent. Although these insects have been latterly confounded with Berosus, it is clear 
they are abundantly distinct. Besides the species here described, I am acquainted with 
only two others that can be assigned to the genus Deralius: both are undescribed ; and 
one is from Colombia, the other from Brazil. I have no doubt, however, the very rare 
* North-American Berosus altus, Lec., is a Derallus; indeed Dr. Horn, in describing and 
discussing this insect (Trans. Am. Phil. Soc. xiii. p. 124), has already pointed out that 
it should probably be generically separated from Berosus. 
1. Derallus angustus. (Tab. II. fig. 16.) 
Lateraliter valde compressus, longitudinaliter convexissimus, superne viridi-eneus nitidus, subtus piceus, pedibus 
rufis ; antennarum basi, palpis pedibusque anterioribus testaceis ; elytris sparsim sat fortiter sed parum pro-- 
funde punctatis, versus latera substriatis, striis conspicue punctatis. 
1 . 
Long. 13, lat. 4, alt. ? lin. 
Hab. GuateMALA, Paso Antonio 400 feet (Champion). 
Head moderately closely and coarsely punctate. Thorax shining and almost 
impunctate, except for a few punctures near the sides. Elytra near the outer margin 
finely striate, the strie coarsely punctured, and the interstices somewhat sparingly and 
coarsely punctate; after the fifth stria those nearer to the suture become very indistinct, 
so that the sutural region appears for a broad space impunctate, except quite at the 
apex. 
The laterally compressed, excessively convex form of this insect is extremely peculiar ; 
the under surface is flat, all the convexity being above. 
BEROSUS. 
Berosus, Leach, Zool. Misc. iii. p. 92 (1817). 
Enoplurus, Hope. 
This genus, as I have remarked in speaking of Derallus, has latterly been mixed with 
