Il8 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 Millstream, 

 New Brunswick, is found a very similar form. There seems to be 

 more variation in the form of the glabella, this often becornmg 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- 

 gidium 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.pidchelliis, 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 XIII, Fig. 4) 



In 1842. Conrad described LicJias 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 L. Trentonensis. 



For the sake of comparison we have oudined (Plate XIII, fig. 8,) 

 the glabella and accompanying parts of Lichas Treiitojiensis as it occurs 



