268 NEW YORK STATE MUSEUM 



their length ; the free ventral margin is straight and subparallel to the axis 

 of the branch ; the aperture slightly introverted and opening within a 

 shallow excavation, that occupies one fourth to one third the width of the 

 branch and one fourth the length of the free ventral margin. 



Position and locality. In a layer of the Normanskill shale at Glenmont, 

 N. Y. associated with Didymogr. sagitticaulis, Dicranogr. 

 furcatus, D i p 1 o g r . f o 1 i a c e u s , C 1 i m a c o g r . parvus, C r y p - 

 togr. tricornis and Lasiogr. mucronatus. Besides two sepa- 

 rate specimens, a slab from the same locality has been found in the New 

 York State Museum, bearing this as the prevailing form [see pi. 15, fig. 5]. 



Remarks. Only one of the type specimens possesses more than two 

 symmetric pairs of secondary branches, all the others have developed only 

 the first pair on either side of the center of the rhabdosome, and some have 

 none at all. In those with but two pairs, the secondary branches are very 

 short, while the stipes are apparently preserved in full length. These facts 

 would indicate that the secondary branches lagged much behind the stipes 

 in their development. 



PLEUROGRAPTUS Nicholson 



The Utica shale of New York has furnished a single specimen repre- 

 senting the monotypic genus Pleurograptus, and this is so fragmentary that 

 it is little suitable to serve as basis of an accurate description of the genus. 

 We therefore insert here the diagnosis of the crenus, given in the Mono- 

 graph of British Graptolitcs at the hand of abundant material. 



Polypary bilaterally symmetrical, consisting of two uniserial main stipes, 

 which diverge from the sicula at angles slightly exceeding 180", and from 

 one margin (or both) of which numerous, usually irregularly disposed, 

 secondary uniserial branches are given off. These secondary branches may 

 be simple or compound. 



Thecae of the type of Leptograptus. 



The New York specimen | pi. 15, fig. 1 ] shows the arrangement ot the 

 secondary branches on one side of the main stipes and of the tertiary 

 branches on one side of the secondary ones ; as well as the slender character 

 of the whole rhabdosome and the leptograptid form of the thecae [see 

 fig. 186]. 



