NATURAL SCIENCES OF PHILADELPHIA. 391 



with the inner edge of the pterostigma, and exhibiting a tendency to run 

 parallel with the adjoining cross-veins. Antecubitals 14 15 ; postcubitals 

 12 13. Two discoidal areolets, commencing with 2 before, with 3 behind. 



Length , 62 mill. Alar exp. $ , 81 mill. Abdomen , 45 mill. One 

 mature 9> c? unknown. 



Besides the somewhat smaller number of antecubitals (14 15, instead of 

 16 19), the species varies from the characters of Macrogomphus only in the 

 5th antecubital cross-vein being robust, instead of the 7th, the membranule 

 being rather pale dusky than black, the absence of a protuberance on the 

 middle of the occiput, in having only a single subobsolete pale dorsal stripe 

 on the dorsum of the thorax instead of two, and no stripes at all on the pleura 

 instead of two yellow ones, in the abdomen being scarcely annulate with yel- 

 low in which respect it agrees with parallelogramma and differs from annu- 

 latus, the unique specimen of rohustus having lost its abdomen and in the 

 femora being normally dilated, and not merely dilated towards their tips. All 

 the femora, as in Macrogomphus, are armed with irregular short teeth beneath, 

 not disposed in rows, and the posterior ones are armed on each side towards 

 their tips with a regular row of spines, as usual in 9 Gornphus, and as is said 

 to be the case in M. annulatus. The posterior tarsi are about four-fifths the 

 tibiae, the others about three-fifths. It is scarcely necessary, I hope, to add, 

 that the triangles of the wings are all free from cross-veins. 



From the most exact measurements I am able to make, abdominal joints 6 

 10 are respectively 5 J, 4|, 3f, 5^ and 1 millimetres long, 3 6 being the 

 same length, so far as the eye can judge. 



There is the same disproportionate elongation of the 9th joint in Macrogom- 

 phus, which, as is remarked in the Monographic (p. 941, " is a unique fact 

 among the Odonata." In that subgenus joints 3 6 are equal, 7 is a little 

 shorter, 8 is only half as long as 9, 9 is longer than even any one of 36, and 

 10 is scarcely one-sixth of 9. {Mon., p. 87.) Again, of the three Asiatic spe- 

 cies at present placed in that subgenus, two only are known in 9 > and in 

 both these two special mention is made of the vertical vesicle being curved 

 as in our species, and having a small tooth at its extremities, just as is the 

 case in spiniceps. {Macr. parallelogramma 9> Mon., p. 80, and compare Plate 

 V, Fig. 5 ; Macr. annulatus 9> Mon., p. 92.) The front, too, in all three spe- 

 cies is said to be obtusely angulated, and but slightly projected ; and in annu- 

 latus the long 9th abdominal joint is described and figured as being tapered at 

 the tip precisely as in spiniceps, and is said to be "excavated" beneath, pro- 

 bably just as in our species. Other striking points of resemblance are, the 

 costal not being yellow, the imperfect prolongation of the internal side of the 

 pterostigma, the extreme length of the pterostigma, the large number of ante 

 cubitals, and the shortness of the posterior legs, which in Macrogomphus are 

 said to attain only the middle of the third abdominal joint, just as is the case 

 in spiniceps mihi. Although Macrogomphus has hitherto only occurred in Java 

 and Hindostan, and although, as has been already seen, there are several 

 minor characters in the circumscription of that subgenus chiefly, however, 

 characters drawn from colorization which do not at all suit spiniceps, yet, I 

 think, we can scarcely avoid considering this species as a Macrogomphus, or at 

 all events as the American analogue of that most remarkable Asiatic form. 

 The full measurements, which will be found a few pages below, along with 

 those of the $ of two Asiatic species, agree closely with those two species, 

 except in the length of the posterior femur, where, I suspect, some error has 

 crept into the figures of the Monographic It will be satisfactory if, on the 

 discovery of the tf spiniceps, its abdominal appendages should be found to be 

 like those of $ Macrogomphus. 



Gomphus spinosus, Selys. (Des Plaines river, near Chicago ; not hitherto 

 found north of Georgia.) G. fraternus, Say ! 



Gomphus vastus, Hagen MS. ! n. sp. tf Greenish yellow. Head with the 

 1862.] 



