NATURAL SCIENCES OF PHILADELPHIA. 163 



Ilalobasna, " Is. Geoffr. 1836," Bon. C. A. 1855, ii. p. 193. (?Type P. casrulea, 

 Gm.) 



Chs. Bill provided with a few laminated serrations at the sides of the base 

 of the upper mandible, just within the commissural edge of the upper mandi- 

 ble ; in length slightly less than the tarsus, equal to the inner toe without its 

 claw; slender, compressed throughout, a little higher than wide at the base. 

 Superior lateral sulcus well marked, nearly straight ; inferior shallow and in- 

 distinct. Unguis of upper mandible small, short, only moderately convex. In- 

 ferior unguis acute, much decurved, the gonys very concave, the ramal outline 

 straight. Interramal space fully feathered. Nasal tubes only a fifth the length 

 of the culmen, short, narrow, elevated, compressed, not carinated, terminally 

 obliquely truncated; nares narrowly oval. Folded wings reach far beyond tail. 

 Tail contained rather more than 2\ times in the wings from the carpal joint ; 

 square, with no graduation of the lateral feathers: all the rectrices so broadly 

 rounded as to be nearly truncated. Tarsus equal to middle toe without claw ; 

 outer rather longer than the middle ; but its claw so short as to make its total 

 length rather less than that of the middle. Tip of inner claw just reaching 

 base of middle. 



The principal character which distinguishes this genus lies in the short, 

 square tail; a feature which is quite unique in this family, being found in no 

 other genus of the Procellariida. Its type and only known species is the old 

 ccerulea of Gmelin, a small delicately formed species, whose colors tend chiefly 

 to bluish and white. 



In general features of external form, proportions of tarsus and toes, and par- 

 ticularly the shape of the bill, which is much compressed, this genus is quite 

 similar to JEstrelata, especially to such of its smaller species as mollis and Cookii. 

 Nevertheless, the presence towards the base of the bill of distinct serrated 

 laminae, which constitute the essence of the Prionitic type,* indubitably fix its 

 position among the latter group, to which also it so closely approximates in 

 color. These laminaj only exist for a short distance on either side of the base of 

 the bill ; but still they are quite palpable and decided in character; perhaps as 

 much so as in Pseudoprion turtur or ariel. The small and rather weak unguis, 

 which does not begin to curve almost directly from the unguis, is essentially 

 Prionitic, as distinguished from typical JEstrelatines. The bill though higher 

 than broad in its whole length, is hardly more compressed than in P. turtur. 

 From these considerations, and esteeming, as I believe justly, that the lamina- 

 tions are the essential character of the Prionece. and consequently more weighty 

 than all others, I include the somewhat anomalous genus in this latter group. 

 I regard it as the connecting link between the JEstrelatem, on the one band, 

 through the genus Daption, and the Prionex on the other, towards the true 

 type of which latter it approximates through the subtypical genus Pseudo- 

 prion. 



I quote the reference to Isidore Geoffroy on the authority of Bonaparte, not 

 having the means at hand of verifying the citation. I do not know what spe- 

 cies is typical in the original founding of the genus. If it be the one named 

 Halobsena typica in the Conspectus, then Halobsena is equivalent to, and has 

 priority over my Pseudoprion ; and a generic name is wanting for the /'. cceru- 

 lea of Gmelin. 



Halobsena cosrulea (Gm.) Bon. 



Procellaria ccerulea, Gmelin, S. N. i. ii. 1788, p. 560. Latham. Ind. Orn. 1790, 



ii. p. 827. Gould, Birds Aust. pi. 52, and of authors generally. 

 Halobsena ccerulea, Bonaparte, C. A. 1855, ii. p. 193. 



: ... 



* In some genera not of the Prionere, e. g. Daption, Ossifraga, etc., there are to be found along 

 the inner border of the cutting edge of the upper mandible, a series of ruga? or alternate depres- 

 sions and ridges, obliquely placed. These, however, are part of the mandible itself, and by no means 

 distinct elements, and therefore are radically different in morphological character from the lami- 

 na? of the Prionex. 



1866.] 



