512 VHOCEEDINdS OF THE NATIONAL MUSEUM. vouxxi. 



K'. A larj^o spocios, nioro than 70 mm. wide. Lower marfrin of 



ft'ont not tiilx^rculiitc henrioi 



J'. (Jariipacc) coiirHoly uraiiiiliito. 



K. MeiMiH of niiixillipod narrow, Hubtriaugiilar, ontor margin 



Htraight or nearly ho .piriii'mua 



K'. Merns of maxillipud b^oa(l(^r, Hulxiuadrilatcral, on I or iiiiiij;iu 

 arcuate to tho diHtal oxtroniity. 

 L. Sixth and soventh Htiginontw of al)domon of male of ocjual 

 length; appondagoH of lirHt Hogmont with extremity 



very hirge and v(irtioally {!om[)re88ed hocourti 



L'. Sixth Hegnu^nt longer than Hcventli; ap)tendageH of the 

 jouj/i groiii* lamtUiJroitK 



UKLAI'lON OK Hl'ICCIICS OK I'SKUDOI'II ICM'IIUSA TO ONK ANO'I'IIKK. 



Th(i {^emis I'scuifothdplinsa now contains 42 spec.ieH, 17 of wliicli are 

 hero (lescribtMl for tlie first tinio. A iiey to a genus in which the varia- 

 tions arc so sliglit as in Pseudothelphusaiii necessarily injperfect. The 

 character of tlui front oilers th(i most satisfactory basis for a, primary 

 division, l^^ven here there are species of doubtful position. I^'or exam- 

 ple, /*. vertimlis forms a link between section A, front without a supe- 

 rior nnirjiin, and A/, fiont with a superior margin, as, although its IVont 

 is vertit-al, thii superior margin is not sharply outlined. Under the 

 species with smooth superior margin, P. tumimanun shows a transition 

 to species with keeh^d fronts, as its superior margin is very well marked, 

 api)roaching a. keel. Tiie forms intt^rmcdiate betwecui section A, front 

 without a superior marginal lino, and section A', ii, C, superior margin 

 tuborc/ulato, are /*. (('iiadorensis and /'. nohilii. The former lias tlu^ sur- 

 face of tlu^ front <roars(5ly granulate, but witlnuit a distinct miuginal 

 lino; the latter has a distinct line:, feebly granulate. Under the group 

 with superioi- margin tubciculate, we ha\o /'. fossor and /'. xanttm 

 inclining toward s|)e('ios with keeled fronts. 



It is a notabh^ lac-t that the morns of the nuixillij)eds of southern 

 species dillcrs fro'm that of northern species. In the former the merus 

 has a subtriangular shape, its outer margin concave or straight or 

 rarely slightly convex and forming an aiigh* with the anterior nuirgin. 

 Jn tht^ latter the merus is subquadrato, and its outer margin is convex 

 and curves gradually into the anterior nmrgin. The first form of the 

 merus is found in niarropa, pJami., ecuadorvusls^ lindifiiaiKt, rliilnisis, 

 hoiiricrij iiohilii, conradi, hatrici, and peruviana, all Soutli American 

 species inhabiting ('olondua, l^.cuador, Peru, and Holivia. The second 

 form of merus is found in all North American and W<'st Indian spe(!ies 

 and in tlu^South America n species _r/a/'wan/,/i'>,s',s'(>/', and denticiitala, which 

 inhabit the northern border of South America (Venezuela and (Juiana). 

 Two of this group, >•/(■// moM^/i and .rantitsi, axieml as far south as Colom- 

 bia. /'. colomhiana has the merus intern)edia,te between northern and 

 southern forms; its range extends northward to Mexico. The meri of 

 7'. rcllcxij'rons (Upper Amazon) and /'. a(/assizii (Para) are also inter- 

 mediate. That oi' wquatoriaiis is unknown to me. 



It is imjmssiblo to correlate this dillerence in the maxillipeds with 



