ii8 
BULLETIN OF THE LABORATORIES 
have seven segments. But the drawing of an enlarged specimen rep- 
resents seven segments very plainly, and suggests an eighth, and even 
a terminal indistinct tenth one by means of the shading. 
In North America, in the St. John’s Group at Ratcliff’s Midstream, 
New Brunswick, is found a very similar form. There seems to be 
more variation in the form of the glabella, this often becoming more 
or less distinctly lobate on either side. The lateral lobes always ap- 
proach to within a short distance of each other anteriorly, being sepa- 
rated by a deep groove rather than by a vacant space. The terminal 
spines of the glabella is also extremely variable, being quite short and 
rather blunt, or equalling two-thirds the length of the glabella, when 
it is very slender posteriorly. The edge of the margin often presents 
the milled appearance noted in the European form, this varying to a 
series of closely set tubercules. The middle lobe of the pygidium 
usually presents nine well marked segments and under favorable cir 
cumstances some of the finest specimens will show a tenth quite dis- 
tinctly, and even faint indications of two more. Both head and py- 
gidiu.m are covered with minute granules. 
Mr. Walcott, in his excellent monographs of our Cambrian fauna, 
referred the American specimens to the Welsh species, with a certain 
reservation on account of variations observed, and suggested the ap- 
plication of the name proposed by Mr. Hartt, M.pidchellus^ in case 
they were found to be distinct. Our own investigations lessen, rather 
than increase the differences then observed.. 
CINCINNATI GROUP. 
Lichas Halli, sp. n. 
{ Plate ^\\\, Fig. 
In 1842. Conrad described Lichas Trentcnensis from the Lower 
Silurian rocks of New York. In the first volume of the palentologi- 
cal reports of that state. Hall re-described it and at the same time il- 
lustrated it in the accompanying plates. Among the illustrations on 
plate 64, figure le, is a specimen from the vicinity of Cincinnati, and 
manifestly distinct from the typical forms of Z. Trentonensis. 
For the sake of comparison we have outlined (Plate XIII, fig. 8,) 
the glabella and accompanying parts of Lichas Tre?itonensis as it occurs 
