1873.] 115 [Brewer. 



Dr. Brewer made some remarks on the Hermit Thrushes, 

 under which name he designated those species of Turdus 

 belonging to the subgenus Hylocichla. 



Eight species of the group were recognized by the speaker : — 

 mustelinus,pallasi, nanus, auduboni (zzz silens of Swainson), fuscescens, 

 sivainsoni, ustulatus and alicice. Prof. Baird, however, would admit 

 only five of these forms to specific rank, uniting nanus and auduboni 

 with pallasi, and swainsoni with ustulatus; and with these two last Mr. 

 Allen also joins alicice. Dr. Brewer could not believe in the propri- 

 ety of these views. Turdus alicice, he said, differs from T. swainsoni 

 in coloration, size, time of migrations, song, distribution in the breed- 

 ing season, and in the nests and eggs. T. ustulatus has more claim 

 to be considered a western race of swainsoni, but there are constant 

 differences in habits as well as in plumage, which he thought entitle it 

 to be treated as specifically different. 



The same is also the case with nanus, and with auduboni. He was 

 also still inclined to regard these as sufficiently distinct from pallasi to 

 be regarded as separate species ; especially as from the general law 

 of size in northern and southern varieties of one species, we expect 

 the southern forms to be smaller than the northern, and, therefore, if 

 T. nanus is a race of pallasi, being the northern race, it should be 

 larger instead of smaller. If Dr. Cooper's account of its nesting 

 and eggs is correct, we have still stronger reasons for its specific rank. 

 Prof. Baird, however, conjectures that Dr. Cooper was mistaken, and 

 that the nests, supposed by him to be those of T. nanus, really be- 

 longed to T. ustulatus, and this conjecture is partially confirmed by 

 the fact that skins from Dr. Cooper referred to T. nanus, prove to be 

 actually skins of T. ustulatus. 



In regard to T. auduboni, we meet again this anomaly. To be a 

 race of T. pallasi this bird, being a southern resident, ought to be, by 

 the law just referred to, a smaller bird than T. pallasi; instead of 

 which it is larger. T. pallasi is a ground -builder, never known to 

 build anywhere else. The only nest of T. auduboni ever found was 

 built in a tree. Then again, T. auduboni is a constant resident all 

 the year of the temperate regions of Vera Cruz, where T. pcdlasi 

 is only a resident in the winter months. 



Dr. T. Sterry Hunt gave some account of the crystalline 

 rocks of the Blue Ridge, and their decomposed condition, as 



