PTENIDIUM. 149 
narrow, fringed on both sides with very long movable sete. Antenne usually long and slender, 11- 
jointed, with the two basal joints very large, the intermediate generally very long and slender, and the last 
three forming an elongate moniliform club, ornamented with long verticillate sete. Palpi: maaillary long, 
4-jointed, with the third joint very large, ovate, not truncate; apical joint long, acicular, and recurved ; 
labial very long and very slender, arising from broad, transverse, labial processes, 3-jointed, with the apical 
joint small, conical, and acuminate. Prosternwm moderate; episterna small and narrow; epimera small 
and distinct, not enclosing the coxal cavities; coxal cavities oval, contingent, and marginal. Mesosternum 
rather large, elevated into a rather flat, subquadrate carina between the coxe; episterna small, humeral ; 
epimera very large, extending to the coxal cavities; coxal cavities circular, separated by the carina. 
Metasternum very large, extending to the sides of the body, moderately produced between the posterior 
cox ; episterna concealed by the elytra, with their interior apical angles alone visible ; .epimera wholly 
concealed by the elytra. Venter composed of seven segments nearly equal to each other in length, the 
apical segment simple (the apical abdominal segment is sometimes dentate at its apex, but this is only 
visible on the underside). Zegs generally long and slender, with the posterior cox small and very slightly 
laminate; tibie sometimes dilated; tarsi 3-jointed, with the two basal joints very minute, and the third 
very long and very slender. 
The species of Péenidium are readily distinguished from all other Trichopterygide by 
their ovate, very convex form, and brightly polished surface. Among the new species 
discovered by Mr. Champion, P. strangulatum is remarkable for the excessive contraction 
of the base of the thorax and of the shoulders of the elytra—at the point of junction of 
these parts its body is as nearly divided into two as are the articulations of the club of 
its antenne; but in other respects it does not anatomically differ from its congeners. 
Ptenidiwm contains a large number of described forms, mostly from Europe or North 
America. The following table will assist in the identification of the Central-American 
species known to me :— 
Shoulders of the elytra strongly contracted . . . . . . . . . strangulatum. 
Shoulders of the elytra not contracted. 
Base of the thorax with four fovez. 
Thoracic fovee very small. . . . 2. ee 1 eee «0beSum. 
Thoracic fovez large. 
Scutellum deeply punctured. . . . . . . . . . foveatum. 
Scutellum scarcely punctured . . . . . . «© © tgnobile. 
Base of the thorax without fovese. 
Colour deep black; size large. . . . . . 2. 1. we onttens. 
Colour rufo-piceous; sizesmall . . . 2. 1... ee) tmpunctatum. 
1. Ptenidium strangulatum. 
Pienidium strangulatum, Matth. Trans. Am. Ent. Soc. xi. p. 148°. 
Elongatum, ad humeros strangulatum, valde convexum, glabrum, nitidissimum, nigrum; capite magno, antice 
producto; oculis magnis, prominentibus; pronoto parvo, transverso, quam caput parum latiore haud 
longiore, ante medium latiore, ad basin fortissime contracto, glabro, nitidissimo, foveis quatuor equidistan- 
tibus valde indistinctis ad basin atque duabus utrinque ad angulum basalem pariter indistinctis notato, 
lateribus late marginatis, valde rotundatis; elytris ovatis, convexissimis, ad humeros atque apices pariter 
et valde attenuatis, ante media latioribus, nigris, apicibus atque humeris rufis, glabris, nitidissimis, stria 
abbreviata remote punctata ad suturam utrinque impressis, apice modice rotundato; pedibus gracilioribus, 
. : . . : . oo. 5-7 7: - “7° 
lete flavis ; antennis modicis, flavis, clavis obscurioribus. Long. corp. “4 lin. =0°75-0°87 millim. 
