60 DR. LEIDY ON THE HISTORY AND ANATOMY OF 



SPECIES. 



Pertiiostoma testaceum. Body spatulate-ovate, testaceous ; thighs and tibiae with three distinct maculae ; 

 superior surface of abdomen black, with the edges testaceous ; lateral margins of the prothorax com- 

 pressed, sub-emarginate ; elytra levigate with the exception of the round patch of pubescence, at the 

 posterior internal angle of the coriaceous portion ; caudal setae three-fourths of a line in length. Length 

 eight and a half lines, breadth four and a half lines. 



Found in stagnant waters in Pennsylvania, <fcc. 



P. AURANTiAcuM. Pale testaceous, thighs indistinctly maculated ; lateral margins of the prothorax sub- 

 emarginate ; superior surface of the abdomen deep black, bordered by orange passing into the testaceous 

 colour of the edges ; caudal setae one and one-fourth lines. Length eleven lines, breadth five lines. 



Found in the same situations as the preceding. Var. immaculatum. Pale luteus, no maculations. Found 

 with the latter. 



Imperfect stages of Pertiiostoma. The larva and pupa are very like those of Belostoma : oval in shape; 

 upper part of the abdomen testaceous, with the lateral margins maculated with black, under surface 

 pubescent ; tarsi with single articulation and two ungues. 



The species of Belostoma and Pertiiostoma, are found in lakes, ponds, ditches, or 

 other tranquil waters. Possessed of considerable strength and activity, they roam 

 about almost undisputed masters of the place. Not only do other aquatic insects 

 become their prey, but the mollasca, smaller Crustacea, and small frogs and lish. 

 Dr. T. B. Wilson informed me, that a workman upon his farm brought to him a 

 specimen of ^. americana, caught in a small stream, near which he had been at work, 

 and which had a sun-fish {Pomotis vulgaris) twice its size struggling within its grasp. 

 A similar instance has been met with by Prof. S. F. Baird, of Carlisle. In the 

 Encyclopaedia Loudinensis, is an engraving of the pupa of B. grandis, luxuriating 

 upon the juices of a small frog, and I met with a somewhat similar instance under 

 the following circumstances. I had in a large basin of water some specimens of 

 Perthostoma, a number of other aquatic insects, a leech, {Hinido decora) and a 

 frog {Rana hatecina) two and a half inches long; these I was in the habit of daily 

 examining, when, to my astonishment, one day, I saw the leech attach itself to the 

 frog, and shortly after, while the latter was still possessed of considerable activity, it 

 was attacked by two individuals of Perthostoma, under which powerful combination 

 the poor animal was soon destroyed. I have seen Perthostoma attack the insects 

 Gyrinus, Hydrophilus, Notonecta, larvae of Libellulce, &c. The hard shelled insects it 

 destroys by puncturing them at the articulations. A larva of B. americana, which I 

 took in Lake George, N. Y., was at the time leisurely appropriating to itself the 

 fluids of a Limnea clodes. I have frequently observed Perthostoma destroy the 

 mollusca Physa, Limnea, and Phnorbis, and it has afforded me much amusement to 

 notice the larvae, shortly after escaping from the egg, seize upon a Planorbis parvus 

 or young Physa, with as much ease as if they had been schooled in the process a long 

 time. Dr. R. E. Griffith informed me that, in Maryland, he frequently noticed a 



