S. W. Ford—Development of Olenellus asaphoides. 129 
ma* (Billings sp., or a species which I am unable to distinguish 
from this form by any good characters), O. nitida, Lingulella 
celata, and asmall species of Orthis yet undescribed. This latter 
species is about one-third smaller than Orthis Billingsi of the 
Acadian groupt which it otherwise much resembles, except 
that the ribs do not dichotomize as in that species. None o 
the specimens yet obtained are sufficiently perfect to admit of 
a full description. 
New York, Oct. 31st, 1877. 
Art, XVIIL—WNote on the Development of Olenellus asaphoides ; 
by S. W. Forp. 
SINCE the publication of my paper giving an account of the 
metamorphoses of this remarkable trilobite,t I have obtained 
at Troy a number of specimens further illustrating and confirm- 
ing the fact of the metamorphoses. Among the more impor- 
tant of these is a beautifully preserved cephalic shield showing 
the manner in which the appendages that I have called the 
inter-ocular spines were finally lost. As this specimen supplies 
one of the most important links in the demonstration and ully 
confirms what was inferred from the structure of previously 
known specimens representing other phases of the development, 
the more interesting features which it presents may be briefly 
noticed at this time. : 
he specimen in question is almost exactly intermediate 
between the forms represented by figures 3 and 4 of my former 
paper. Excepting the neck-furrow and the second pair of fur- 
rows in advance, none of the glabellar furrows reach the median 
line; while the inter-ocular spines, still further reduced in size, 
are seen to be entirely cut off from the swollen spaces between 
the eye-lobes and glabella, by the furrows immediately within 
the eye-lobes extending completely across them, and uniting 
with the marginal furrows. There can be scarcely a doubt but 
that the next moult would result in a bead destitute of these 
appendages, as in fact, we find the forms next in order of in- 
creasing size to be. The dwarfed proportions of the appendages 
lead also to the conclusion that they are examples of atrophied 
Organs, as has likewise been suggested to me by M. Barrande. 
I know of no instance of this—the suppression of spinous 
* This Journal, Ma: 
me ? iV, 187 . 355. 
{ Acadian Geol., Tigaee 1868, p. 644. Also Dana, Man. of Geol., 1874, p, 
