REVILLAGIGEDO AND TRES MARIAS ISLANDS. 19 
penetrate a man’s clothing, and were found to be even more unpleasant than the 
cactus thickets on Clarion Island. 
Roca Partida, or Divided Rock, lies 65 miles north-west of Clarion, and is the 
fourth of the group. It is of considerable elevation and has the appearance of a ship 
under sail. 
The number of species of birds observed by Mr. Anthony are as follows :—Socorro 
(24—13 of which were generally distributed land birds), Clarion (17—10 of which 
were land birds), San Benedicte (11—including 3 land birds). 
TRES MARIAS ISLANDS. 
As in the case of the Revillagigedo Group, neither Salvin nor I visited the Tres 
Marias Islands; but Alphonse Forrer collected in Maria Madre on our behalf and 
obtained a large number of specimens. For a description of the physical aspect of 
the islands we ate indebted to Mr. E. W. Nelson, who wrote a ‘General Account 
of the Tres Marias Islands with Reports on Mammals and Birds,’ supplemented 
by Notes by other authors on the Reptiles, Crustacea, and Plants (North American 
Fauna, No. 14, 1899). 
The islands are situated about 65 miles off the west coast of Mexico from San 
Blas, between lat. 21° and 22° and long. 106-107, and consist of a group comprising 
Maria Madre, Maria Magdalena, Maria Cleofa, and San Juanito, arranged in a north- 
westerly and south-easterly direction. 
About 20 miles from the mainland lies the small island of Isabel, about 1 mile 
long and 150 feet high. It chiefly consists of the remains of an old volcano, and 
a small crater still occupies the centre. ‘There is evidence of its having once been a 
much larger island, though now apparently sinking. ‘The soundings in the channel 
between the islands and the mainland gradually deepen to nearly 300 fathoms, but 
west of the group the sea bottom falls rapidly to over 1500 fathoms. | 
Maria Madre, the largest island, measures 8 by 15 miles, and rises over 2000 feet 
above the sea. The interior is occupied by a mountain ridge extending almost the 
whole of its length, but descending to a gently sloping area at each end. ‘The eastern 
side has the longer slope, while the western or seaward face is much more abrupt, 
thus corresponding with the formation of the mountains parallel to the coast on the 
adjacent mainland. Both slopes are scored at intervals with cafions, which usually 
descend ina nearly direct line to the sea, and along the lower slopes of which, Spanish 
cedars and wild figs are grown, certain trees attaining a great size. Generally speaking, 
the forest is low and scrubby near the shore, but increases in luxuriance farther up the 
slopes. In its primeval condition before the advent of wood cutters, a fine example 
of typical forest growth must have been presented here. 
North of Maria Madre, and separated by a channel 4 miles wide and 5 or 6 fathoms 
D2 
