RANK OF CIRCULAR GROUPS. 345 
shell-fish, when properly restricted, will be found groups 
of the same value, that is, if we consider the Mollusca 
as a class; but if we view it, with Mr. MacLeay, as a 
sub-kingdom, then they must be considered as classes. 
(426.) We shall illustrate the rank of T’ribes from one 
of the most perfect, and, now, the best-established groups 
in zoology, namely, the order of Jnsessores, or perching 
birds. This most extensive order has been correctly 
stated* as the only one in the ornithological circle which 
contains tribes, designated and characterised as follows : 
—1. Conirostres, with a conic bill, and pre-eminently 
perchers. 2. Dentirostres, or perchers of prey, with 
sharp claws, and living chiefly upon insects. 3. Fissi- 
rostres, with large heads, flat bills, and weak feet, as the 
swifts and swallows. 4. Tenuwirostres, with small eyes 
and mouth, and long bills, like the humming-birds. 
And, lastly, 5. The Scansores, or climbers, which brings 
on the woodpeckers, parrots, and cuckoos. These are the 
only tribes, or groups between families and orders, to be 
found in the class of birds. But in most of the orders 
of the Ptilota, or winged insects, tribes are very preva- 
lent. The lepidopterous order, for instance, has the five 
tribes of Diurnes, or diurnal butterflies ; Sphingides, or 
hawk-moths ; Bombycides, or silk moths ; Phalenides, 
or geometric moths; and Noctuides, or night moths: 
although, as Mr. Kirby truly remarks, the primary di- 
vision of this order is into three; the three aberrant 
tribes forming one circle. In the coleopterous order the 
tribes are very large, of which we shall cite the Lamelli- 
cornes (Scarabeus Lin.), or herbiverous beetles, and 
the Predatores, or rapacious beetles (Chilopodomorpha 
MacL.) as examples, to be hereafter verified. It is ques- 
tionable whether tribes occur in the aberrant orders of 
either the Annulosa, Mollusca, Radiata, or Acrita, any 
more than they do in the aberrant orders of birds. At 
all events we have not yet detected them. 
(427.) Families are comprehended under tribes, when 
the latter exist ; otherwise, as in the case of the Rasores, 
* Linnean Transactions. 
