( 104 ) 



j)atcli of siiberoct scales. Poiiis-slieatli with a very miuute apical lobe indicating 

 the tootli ol'the allied Sphingidae. 



?. Auteuua almost c_ylindncal. 



Hull. Jlexico : Honduras : tiroliablv more widely distributed in Central America. 



XXVI. ISOGRAMMA gen. nov.-Typns : Imgeni. 



Ceratomiii, Grote {mm Harris, 1839), Bull. Buff. Soc. Nnt. Sci. ii. p. 149 (1874). 



Daremma, ij. (won Walker, 185G), I.e. iii. p. 224 (1877). 



S/ihwiC, Strecker (no« Unn4, 1758), Lep. Rhop. Uet. p. 127 (1878). 



(J ?. Antenna of ? with a row of prolonged ciliae. Foretibia spinose at end ; 

 first segment of foretarsns little longer than second, with some long stout spines ; 

 niiiltibiii with a few spines at the very end, midtarsns imthout comb ; paronychium 

 and pulvillus jy;-e«(?«<. Tubercle of labrnm with sharp edge. 



S. Tenth tergite prismatically compressed, sulcate above, except at convex 

 apex, convex beneath, becoming carinate at end, apex curved downwards, pointed 

 in side-view, obtuse in frontal view ; sternite mesially divided into two conical 

 pointed processes (PI. XXVIII. f. 4) which are cnrved upwards at end. Clasper 

 broadly sole-shaped, widest l)efore middle, apex broadly rounded, a short, high, 

 subdorsal fold, ending where the clasper widens dorsad ; harpe (PI. XL. f. 3) 

 scaled on surface as in CItlaenogramma, a pointed, finger-like, ventro-distal 

 process, and a broad, short, rounded upper lobe, dorsal edge of har])e irregularly 

 dentate. Penis-sheath armed with an apical, conical, horizontal tooth which slants 

 distad a very little. 



? . Vaginal plate nearly as in Chlaenogramma , but the ridge before the mouth 

 of the vagina mesially deeper sinnate ^nd somewhat impressed at the sinus 

 (PI. XX. f 11). 



Larva covered with dispersed, transversely seriated grannies, side-bands 

 bordered with red ; head granulose (snb-triangnlar ?). 

 Hab. Texas. 

 One species. 



In the shortness of the foretibia and first segment of the foretarsns the only 

 species of this genus agrees with the species of Ceratomia, and in the preservation 

 of the pulvillus with Chlaenogi-amma, while it differs from both genera in the 

 foretibia and the extreme apex of the midtibia being armed with spines. The 

 spinosity of the tibia is an advanced character, not acquired by Ceratomia, while 

 the pulvillus is an ancestral structure already lost in Ceratomia. Therefore the 

 genus Jsogramma, though closely related to Ceratomia, is in one respect more 

 advanced than this, and in another it lags one step behind. This clearly sliows 

 that l.fogrnmma and Ceratomia represent two divergent lines of development. 

 With a little jwwer of construction it is not difficult to conceive that one and the 

 same link is missing both between Ceratomia and GIdacnogramma, and between this 

 and Tsogramma, this link being the common ancestor of Isogramma and Ceratomia, 

 characterised by the possession of a pulvillus, not-spiny tibiae, and short and 

 strongly armed first segment of anterior tarsus. From this ancestral form Imgeni 

 branched off by acquiring spinose tibiae (and in ? andromorphic antennae), 

 preserving the pulvillus, while Ceratomia became differentiated by losing the 

 pul villus, Imt keejiing the unarmed tibiae. A further differentiation into three 



