GRAPTOLITES OF NEW YORK, PART 2 469 



is straight while the other is zigzagged. Roth are seen in some of our 

 compressed specimens [see pi. 31, fig. 8|. They are held in position by 

 " internal cross-ledges," arranged like the cross-pieces of a ladder [see text 

 fig. 450, 451]. From these proceed strong, horizontal, alternating loops, 

 the lateral portions of which (the "parietal ledges") mark the boundaries 

 of the thecae while the distal portions (the "mouth ledges") form the lower 

 rims of the thecal apertures. Strong ledges also bound the lateral margins 

 of the apertures. There do not seem to be an)' inner partitions of the 

 thecae as in Diplograptus, which Retiolites resembles most in the direction 

 and form of the thecae. 



The perisarcal network consists of polygonal meshes. It is fastened 

 to the parietal ledges but adheres only to their middle and distal portions, 

 while it extends independently over the median portion of the lateral faces, 

 covering and hiding the virgula completely in specimens which are not 

 opened by fracture [see pi. 31, fig. 7]. In such specimens the parietal ledges 

 will be seen to disappear under the network near the median line. 



A sicula has not yet been observed in Retiolites. 



The genotype is R . g e i n i t z i a n u s. Of this our American form is 

 but varietally, if at all, different. 



Retiolites geinitzianus Barrande van venosus (Hall) 



Plate 29, figures 7, 8 ; plate 31, figures 6-8 



Graptolites venosus Hall. Pal. N. Y. 1852. 2:40; pi. 17A, fig. 2a-c 

 Retiolites venosus Geinitz. Die Graptolithen. 1852. p. 58 

 Retiolites venosus Hall. Pal. N. Y. 1859. 3:518 

 Retiolites venosus Nicholson. Mon. Brit. Grapt. 1872. p. 42, fig. 12 

 Gladiolites venosus Gurley. Jour. Geol. 1896. 4:79, 308 

 Retiolites venosus Roemer & Freeh. Lethaea Pal. 1897. 1:669, fig. 221 

 Non Retiolites venosus Spencer. 1 Acad. Sci. Trans. St Louis. 1884. 



4:5 6 4, 5 66 ; pl- !- fig- 2 



1 Gurley lias in 1896 \loc. «V.] pointed out that the specimen figured by Spencer as 

 R. venosus (figure copied by Miller) lias no relation to that species and may not be a 

 graptolite. His conclusion is borne out by the material of the National Museum which 

 the writer has in hand. 



