SI8 Dr Johnston’s Contributions to the British Fauna. 
dom, or the simple mineral, is the sole object of Mineralogy ; so 
also, the natural-historical properties of the simple mineral are 
the only ones to which, in that science, we ought to direct our 
attention. It is a general condition imposed upon all sciences, 
that each should contain matter of the same kind only. Every 
information, therefore, that Mineralogy affords, must flow from 
the observation and comparison of' the natural-historical pro- 
perties of simple minerals ; as in mathematics every depart- 
ment of information must arise from the observation and com- 
parison of quantities of the same kind. From a similarity of 
origin in the information, we also infer it to be similar in kind, 
and in this consists the character of belonging to one and the 
same science. The purity of the science also is dependent up- 
on the nature of its constituent objects, as will appear from the 
care bestowed upon the establishment of their general ideas by 
mathematicians, which will, of itself, be sufficient to shew their 
high degree of importance. 
( To be continued.) 
Art. II. — Contributions to the British Fauna. By George 
Johnston, M. D. Fellow of the Boyal College of Surgeons, 
Edinburgh. 
1. CIRRATULUS. 
Cl. ANNELIDES.— Ord. Apodes. 
Char. Body elongated, round, flattened on the ventral sur- 
face ; garnished, particularly on the anterior end, with nu- 
merous long capillary filaments; each ring on each side 
with two setiferous papillse or feet. 
Obs. It will be remarked, that the characters assigned to this genus by 
Lamarck have not been rigorously adopted. Had that been done, the species 
about to be described would have had a doubtful claim to a place in it ; and, 
rather than constitute a new genus, I have not hesitated to give a greater la- 
titude to the generic character, — the more particularly since Lamarck himself 
has recognised the relation which the Terebella tentaculata of Montagu (an 
animal evidently of structure similar to ours) bears to his Cirratulus. The 
following additional characters are common to the two species we have ob- 
served, and which do not seem to have been heretofore described by any Bri- 
tish naturalist. The body tapers a little towards each extremity, and is ca- 
