166 bulletin: museum of comparative zoology. 



PHAETHONTIDAE. 



1. Phaethon rubricaudus Boddaert. 



Phaeton rubricauda Boddaert, Tabl. plan, enl., 1783, p. 57. (Mauritius). 



Three specimens were collected at sea about 600 miles east of the 

 Marquesas Islands in Latitude 10° N., Longitude, 130° W., 2 Septem- 

 ber, 1899. All three are immature. One has the upper parts heavily 

 barred with black, but in the other two these markings are less evident. 

 The red-tailed tropic-birds without doubt are divisible into two or 

 more subspecies, but in the absence of material from many localities 

 needed for a competent review of the forms no attempt is made to 

 allocate the present specimens subspecifically. The fact that all are 

 immature would add to the difficulty of such an identification. The 

 measurements of these birds are as follows : — 



These skins are similar in size to specimens from Laysan Island, in 

 the Hawaiian Group. 



It has been proposed by Mathews (Austr. avian record, 1913, 2, 

 p. 56) to separate the Red-tailed tropic-bird from Phaethon under the 

 generic name Scaeophaethon, on the grounds that it has a longer wing, 

 stronger legs and feet, and shorter tail. Upon careful comparison 

 it is found that all of these characters do not hold. Thus when 

 compared with Phaethon aetherevs, the type-species of the Linnaean 

 genus Phaethon, specimens of P. rubricaudus from Assumption and 

 Gloriosa Islands (north of Madagascar) do have the wings longer. 

 On the other hand red-tailed birds from Laysan Island have the wing 

 equal to or shorter than that of the red-billed species. In other words 

 birds from these two localities, representing only well-marked forms 

 of one species, would be placed in different genera on this character. 

 The feet and tarsi are slightly stronger and the tail is shorter in 

 riihricandtis when series of the two species are compared. There is 

 so much individual variation in respect to length of tail that it is of 

 value only as an average character. In addition there are other 



