734 NEW YORK STATE MUSEUM 



Reteograptus ten tacul atus Roemer & Freeh. Lethaea palaeozoica. 1897. 



Bdl, p.608 

 Retiograptus tentaculatus Ruedemann. ]S". Y. State Paleontol. An. Rep't. 



1902. p.571 



Description. Rhabdosome small (maximal length about 20 mm), elongate 

 elliptic, gradually and sliglitly widening toward the middle, where it attains 

 a width of about 4 mm, and equally narrowing toward the antisicular end. 

 Periderm finely reticulate, the meshes subcircular to subhexagonal. Sicular 

 end provided with two shorter straight and two longer curved lateral 

 spines, which assume a direction subparallel to the axis of the rhabdosome. 

 Thecae placed rectangularly to the virgula, numbering 10 to 14 in 10 mm, 

 each provided with a stout, sti'aight or slightly downward curved spine and a 

 ringlike thickening of the apertural margin. Apertures straight, parallel to 

 the axis of the rhabdosome. 



Position and localities. In the shale exposed at the dam in the Deep 

 kill section, belongmg to the zone with D i p 1 o g r a p t u s d e n t a t u s 

 and in the somewhat older beds at Mt Moreno near Hudson. Hall's material 

 came from the same horizon at Point Levis. Matthew referred a form from 

 the division 8 d of the St John group with doubt to this species. As all the 

 other species of 3 d are those of the Tetragraptus zone, it is not likely that 

 R.. tentaculatus is present in that horizon. 



Hemarlts. Some of the specimens of this species possess a considerable 

 similarity with Glossograptus fimbriatus Hopkinsou, Avhich occurs 

 in the homotaxial EUergill beds of the Upper Skiddaw slates ; they differ still 

 in the smaller length of the spines and smaller number of thecae within a 

 certain space. 



In one specimen [fig.35], which is Avell preserved and which exhibits a 

 distinct reticulation, some of the apertural spines are prolonged into chitinous 

 filaments, which, bending downward, unite with those of the next preceding 

 thecae in a manner suggesting the marginal structure of Lasiograptus. 

 The latter structure according to Tornquist [1890, t.2, fig.27] and Freeh 

 [1897, p.672], consists of the distal, coarsely perforated portions of the 

 thecae. 



