666 NEW YORK STATE MUSEUM 



Tetragraptus (Etagraptus) lentus sp. nov. 



Plate 9, figures 7-10 



Description. Siciila large (2.1mm) and slender. Piimary theca generally 

 budding from the first third of the siciila, this and the next forming right 

 angles with it; narrow, tubular and long (1.6). Secondary branches at 

 first foi-ming obtuse angles, generally about 120", ^vith the primary branches, 

 but later on assuming positions perpendicular to them. Branches narrow 

 and flexuous, maximal width .37 mm, total length not known. Thecae 

 extremely long (attaining a length of 2.4mm), tubular and slightly curved; 

 seven times as long as wide, little widening toward the aperture ; over- 

 lapping not more than one fourth of their length, numbering 6 in 10 mm. 

 Outer wall subparallel to the axis of the branch, forming an angle not 

 surpassing 5" with the latter. Apertural margin straight and perpendicular 

 to the axis of the branch. 



Positimi and localities. Graptolite bed 3 at the Deep kill. On slab with 

 Didymograptus bifid us and Goniograptus geometricus. 



RemarTcs. There is no similar form known to the writer which would 

 invite comparison. Coenograptus gracilis, while readily dis- 

 tinguished by the arrangement of the branches, has very similar thecae and 

 branches. The direction of the secondary branches is in this species the 

 same as in Tetragraptus approximatus Nicholson, which, however, 

 is entirely different in the character of sicula and thecae. 



DIDYMOGRAPTUS McCoy 



The genus Didymograptus was proposed by McCoy [1851, p.9] for 

 uniserial forms, which are bifid from the base. Later Hopkinson separated 

 the forms with solid axes in the branches under the generic term Dicello- 

 graptus. 



We have in the introduction attempted to trace the genetic relationship 

 of the species of Didymograptus, described in this publication, to forms 

 with a greater number of branches; and there discussed the fact that the 

 various Didymograptidae represent the biramous development of different 



