LARUS ARGENT ATUS, HERRING GULL. 620 



detailed heightening tbe probability of the varietal distinction of L. smitlisonianus. 

 Tlie Herring GuUa of both continents differ from such species as glaucm, Icucopterns, 

 &c., in not being truly boreal birds. They migr.nte northward only to breed, and re- 

 turn south as soon as the duties of incubation are accomplished. The American spe- 

 cies, at least, rarely passes beyond Labrador, and is more abundant in its souihern 

 than its northern portions. It is well known that the nearer to either pole is the 

 habitat of a species the more likely it is to range indiscriminately on both hemis- 

 pheres; and, conversely, the more tropical a species the more likely it is, coclerin pari- 

 bus, to be specifically distinct from its transoceanic representative. We can see here a 

 reason why svilthsoniamis may be somewhat different, while L. glaacus, leucopterui, and 

 F. eburnea are identical. This fact is adduced merely to show why we may expect to 

 find the differences which do exist in var. smitlisonianus and are absent in glaucus ; 

 thongh, at the same time, I separate the variety upon its physical characters alone, 

 irrespective of any preconceived theory of geographical distriljution. 



Synonymy. — Laroides argentatoicles, Brehm, appears to include both the European and 

 American bird. His americanns indicates a bird smaller and less robust than European 

 argentatus, and may be consequently inapplicable here. It corresponds more nearly 

 with " californiciis.'' The argentaioides of i3.onaparte's Synopsis, represented as common 

 along the Atlantic coast, may really lefer to ddawarensis. L. afflnis of Reinhardt, of 

 Greenland, I have not been able to identify. 



Anatomical characters. — The month, in capacity, is intermediate between that of Ster- 

 corarius and of Sterna ; the angle of divergence of the mandibular rami being less than 

 in the former, bnt greater than in tbe latter. The palate is quite flat both transversely 

 and longitudinally, being not at all vaulted and scarcely concave, except toward the 

 tip of the bill, where it curves downward with a considerable degree of convexity. 

 The palate is soft and vascnlar to within about an inch of the tip, where it becomes 

 corneous and divided by five or six longitudinal striai. At the commencement of the 

 more vascular jiart of the palate there begins a median elevation; quite broad and 

 without a central ridge, which continues back for more thau two inches. This is 

 everywhere beset with stout, reversed papillte, the largest of which are along the me- 

 dian line". The central elevatitn is bifurcated for nearly its posterior half, to form the 

 opening of the posterior nares, the edges of which fissure are thickly papillate, as are 

 the posterior extremities of the elevation itself. This median longitudinal prominence 

 is separated on each side by a deep sulcus from a lateral ridge. This lateral ridge an- 

 teriorly sinks insensibly into the common level of the palate ; posteriorly it rises up 

 very broad and thick, and, together with its extremity, is papillate. Just external to 

 these ridges are the deep depressions in which the tomia of the lower mandible are 

 received. 



Posterior to that portion of the palate just described, there is a large, vaulted, sub- 

 triangular space, extending quite to the extremity of the palate. This space is 

 bounded anteriorly by the termination of the central median elevation already de- 

 scribed ; laterally by the continuation backward of the lateral ridges ; more posteriorly, 

 where the sides of the triangle come together to form the apex, by a very perfect 

 fringe formed by a single thick-set row of slender, acute papilla:, placed obliquely, 

 their posterior extremities divaricating, their anterior meeting on the median line. 

 The place thus inclosed is quite smooth, being free from sulci or rugse, and presents the 

 orifice of the Eustachian tube. It is fissured along the median line by the posterior 

 continuation of the nasal aperture. The edges of the fissure cannot be accurately co- 

 aptated, as can tliat portion of it more anterior, the portion of the posterior nares con- 

 sequently remaining always more or less patent. The edges of the opening terminate 

 each in a soft papilla. On separating them, the vomer is seen nearly for its whole 

 length, dividing the nasal aperture into a right and left. Posterior to the termination 

 of the nasal fissure is the usual median, longitudinally oval foramen, the opening of 

 the Eustachian tube ; measuring in this species a full fourth of an inch. All around 

 this central smooth portion the mucous membrane of the mouth is thrown up into 

 more or less irregular rugse, mostly longitudinal, and continuous with the ordinary 

 oesophageal folds. 



The floor of the mouth is of a very regularly triangular shape, the sides being 

 scarcely at all concave. The rising up of the tomia of the mandible on either side gives 

 it a very considerable depth and almost perpendicular sides, especially anteriorly. The 

 muscular and other layers composing the floor, are very distensible and elastic. The 

 mucous membrane, in its uudilated condition, is everywhere thrown up into rugse, 

 chiefly longitudinal, except just over the larynx. The muscular layers are well 

 marked, but present notliiug peculiar either in shape or distribution. The tongue is 

 just two inches long. It is stout and fleshy almost to the tip, which is obtuse, flat- 

 tened, slightly bifid. Its dorsum is longitudinally channeled ; its under surface trans- 

 versely convex ; its posterior extremity prolonged into two short, obtuse cornna, whicli 

 are thickly papillate. The triangular, smooth eminence which is borne upon the sur- 

 face of the larynx, measures about an inch in extent by half as mnch in breadth. The 

 opening of the glottis divides it longitudinally for its Svhole length. The rima is quite 



