48 Dr. A. S. Packard, Jr's Revision of the 



unrivalled collections in the charge of this eminent hymenopterist, 

 have been used with great skill and good judgment. 



In agreeing with Dahlboni in separating the Crabronidoe into three 

 sub-families, we do not agree with authors in placing the Pemphredo- 

 ninae between the Philanthinae and Crabroninae. We would rather 

 consider them as nearly parallel groups, of which the Pemphredoninas 

 occupy the lowest position. Psen. a degraded Cerceris t is closely allied 

 to Cerceris, but Stigmus, a degraded Crabro, is also closely connected 

 with Crabro through RhopoJum ; the mass of their characters, how- 

 ever, and the degradational forms existing among them, show plainly 

 their inferiority to the other two sub-families, and their relationship to 

 the Larridoa and Sphegidoa. They seem, as it were, to jump over the 

 Nyssonidre, and ally themselves more closely with the Larridas. Of 

 the three sub-families, the Pemphredoninaj, as seen above, afford the 

 most mimetic forms or " comprehensive types," and by their elongated 

 bodies and general forms, they are more closely related to the lower fam- 

 ilies of fossorial hymenoptera, while in their less essential characters 

 they borrow the characters of the groups above them. 



The Pempredonidae, like many other low groups, have a less number of 

 species, and show greater generic differences than in the higher groups, 

 whose compact cephalized forms afford less room for marked structural 

 variation. Are these low forms made to mimic the higher types simply 

 that they may be preserved in the life struggle, as Mr. Wallace in- 

 fers the tailness Papilionidae imitate the members of the family next 

 below, that the} T may be mistaken for them ? We would grant this in 

 some cases, but such groups we must look upon as isolated forms, the 

 connecting links of which have perished in mesozoic times ; and also 

 as comprehensive types,* out of which are elaborated higher genera, 

 differentiated into a larger number of specific forms. But it strikes 

 us that many of Mr. Wallace's so-called mimetic forms are those related 

 by characters of affinity and not of analogy, with the members of the 

 succeeding and lower family. His "mimetic" forms are not, there- 

 fore, what we have called comprehensive forms. Like all closely rela- 

 ted species of true contiguous natural groups, their forms and general 



* This term is synonymous in meaning with the term " synthetic" as pro- 

 posed by Professor Agassiz; only one is derived from the Latin, the other from 

 the Greek. But long before, the Botanist Fries in his most philosophical Essay, 

 used th«- term " synthetic" for such organisms as the apple, which tops the ve- 

 ^.■luble series, combining and concentrating in its single form all the most im- 

 portant characters of the Vegetable Kingdom. We therefore use Prof. Dana's 

 term proposed in his Crustacea of the U. S. Expl. Exped. 1854. 



