INSECTA MADERENSIA. 43 



posterior four are nearly simple. But there is a mucli greater difl&culty in sepa- 

 rating tlie females, since, from then' similarity of outline, the smaller varieties of 

 the former and the larger ones of the latter do certainly approach each other at 

 times very closely, and might almost be supposed, were it not for the great struc- 

 tui'al peculiarities afforded by the males, to belong to one and the same species. 

 Still, even in the case of the females, it is only in these intermediate links, Ijeing 

 the extremes of each, aberrant in the opposite directions, that there is any real 

 difficulty in separating the two, since tyjiicalhj the prothorax of the A. dilaticolUs 

 is so much wider behind, in both sexes, than is the case with that of the A. curtns, 

 and its elytra are so much broader at their extreme base and more attenuated 

 posteriorly (there being moreover scarcely any tendency to the apical excavation 

 which is more or less apparent in nearly all the states of the A. curttis), and the 

 entire insect is so mvich flatter, larger, and more robust (especially in the deve- 

 lopment of its legs), that in its normxd state even the female characters are easUy 

 grasped. But, as touching the externally approxunating varieties of each above 

 mentioned, I must confess that, after a careful examination of more than eighty 

 specimens in my possession, there are but few points on whicli to lay hold in 

 drawing the liiie of demarcation between them ; and I think perhaps that the 

 somcAvhat less truncated ehi:ra and more robust legs of the A. dilaticolUs are the 

 most important facts to be observed, in such sjyecimens, while endeavoiu-ing to 

 identify them. And we may here just remark, that the near resemblance of the 

 insects in question, in these intermediate but fortunately not very numerous 

 female links, does not in any way affect their specific validity, which is already 

 proved to a demonstration by the invariable structiu'al differences in the tiluoe of 

 theu' respective males. And, proceeding therefore on the positive conviction that 

 differences do exist, even though we may not always be able at once to appreciate 

 them, we are compelled to attach the greatest weight to minute (and, in ordinary 

 cases, perhaps trivial) characters which may afford the slightest clue towards a 

 right adjustment of the specimens before vis. 



The A. dilaticolUs is, apparently, much rarer than any of the other Madeu'an 

 representatives of the genus, being found principally beneath stones and logs of wood 

 in the dense ravines of intermediate altitudes, especially towards the north of the 

 island. During my encampment at the Lombo dos Pecegueiros, in July 1850, I 

 captured it in comparative abundance throughout the whole of that remote district. 



31. ArgTitor curtus, WoU. 



A. oblongo-ovatus graciusculus nigro-piceus subdepressus, prothorace subquadrato postice ssepius 

 latiusculo, elytris leviter striatis singulo pucctis duobus sat distinctis impresso, antenuis pedi- 

 busque nifo-pieeis. 

 Mas, nitidus ; tibiis intermediis leviter cun'atis ante apicem intus obscurissime anipliato-distortis, 

 posticis vix eurvatis ad apicem obscure dilatatis. 



g2 



