166 . Hull on the 



Graptolithus extensus. 



Frond probably two-branched ; branches long-linear, varying in 

 width in different individuals from one-twelfth to one-tenth of an 

 inch exclusive of the serratures, and from one-tenth to one-eighth 

 of an inch including the serratures. Serratures oblique, with the 

 extremities slender and nearly erect, mucronate at the tip ; about 

 twenty in the space of an inch ; base of branch scarcely narrowed, 

 showing a few smaller serratures ; surface strongly striated, the 

 striae being preserved in those specimens which are extremely 

 compressed. 



The branches of this species bear a very close resemblance to 

 those of G. octobrachiatits, but an individual in which the base is 

 preserved shows in its peculiar curving and smaller serratures a 

 feature which belongs only to the two-branched forms. The ser- 

 ratures also appear to be more slender, and are slightly closer in 

 their arrangement ; branches of the same size in the two, present- 

 ing respectively eighteen and twenty serratures. 



This species in separate branches of from three to six or eight 

 inches in length, is abundant on some slabs of decomposing gray- 

 ish-brown shale, associated with G. brgonoides, G. nitidus, and 

 others. 



Locality and Formation. — Point Levy ; Hudson River Group. 



Collectors. — J. Eichardson, E. Billings, Sir W. E. Logan, James 

 Hall. 



Graptolithus denticulatus. 



Description. — Frond apparently consisting of two broad branches 

 (the base and junction of which are obscure in the specimen ;) mar- 

 gins defined by a rigid line, beyond which on the inner side are ser- 

 ratures which have the form and character of small denticulations 

 inserted npon the margin of the branch and vertical to its direc- 

 tion, broad at base, abruptly tapering above, and ending in mu- 

 cronate points ; about sixteen in the space of an inch. 



This very peculiar species is readily recognised by the denticula- 

 tions, which have the character of small sharp teeth fixed upon the 

 margin of the branch. These denticles are more widely separated, 

 as well as different in character, from those of any other species 

 observed. 



Locality and Formation. — Point Levy, Hudson River Group* 

 Collectors. — Sir W. E. Logan, James Hall. 



