38 bulletin: museum of comparative zoology. 



Characters. — In general like H. c. cachinnans (Linne), but upper 

 parts paler, browner, and less blackish; under parts varying from 

 soiled white to light buff (warm-buff or even darker in true H. c. 

 cachinnans). 



Measurements. — Type, adult cf ; wing, 270; tail, 204; tarsus, 70; 

 culmen from cere, 22. 



34. RosTRHAMUS sociABiLis (Vieillot). 



Thirteen specimens, two adult and eleven immature, not sexed, 

 all from Vicinity of Paramaribo, February, March, April, May, and 

 December. 



The generic name Rostrhamus Lesson (Traite d'orn., 1830, p. 55), 

 type Rostrhamus niger Lesson, judging from the descriptions of both 

 the adult male and young, applies wholly to the bird now known as 

 Rostrhamus sociabilis (Vieill.). Lesson refers also to Falco hamatus 

 Illiger, Temm., PI. col., but draws his description from specimens in 

 hand, and not from the plates. Plate 61 represents the adult of the 

 species now known as R. hamatu^, showing clearly the short tail and 

 short wing-tip, which we consider generically distinct. But Plate 

 231 depicts the young of R. sociabilis with the characteristic long 

 wing-tip and white upper and under tail-coverts. 



Hamirostrum Sundevall (Avium disp. tent., 1873, p. 109), is simply 

 a substitute for Rostrhamus Lesson; see A. O. U. Code 1908, Canon 

 XXX, p. lix. 



Helicolestes, gen. nov. 



Type. — Falco hamatus Illiger, Temm. PL col., 1823, 1, pi. 61. 



Characters. — Similar to Rostrhamus Lesson, but with a very short 

 wing-tip, the primaries exceeding the secondaries by not over 50 mm. ; 

 tail very short, about 120 mm.; immature plumage slate-gray, not 

 essentially different from adult, except in white barring of tail and 

 primaries. 



35. Helicolestes hamatus (Illiger). 



Seven specimens, adult and immature, not sexed, all from Vicinity 

 of Paramaribo, January, February, March, and December. 



This bird, with short tail and short wing-tip, has not been definitely 

 recorded from Surinam up to this time. August Kappler (Hoi- 



