18 BULLETIN 65, UNITED STATES NATIONAL MUSEUM. 



but a review and also a discussion of the generic characters was pre- 

 sented by Doctor Ruedeniann before the Gurley manuscript came 

 into his possession. To Doctor Ruedemann's excellent work the 

 reader is referred. 



Genotype. — Dktyonema retiforine (Hall). Niagaran (Rochester) 

 shale, New York. 



DICTYONEMA RETIFORME (Hall). 



Gortjonia ? rclcfonnis Hall, liep. Surv. 4th Geo]. Dist. New York, 1843, 

 p. 115, text fig. 1. 



Dictijoiioia ictifonnis Hall, Nat. Hist. New York, Pal., II, is."2, p. 174, 

 pi. 40F, figs. 1 a, 6. — LiNCKLAEN, 14tb Rep. New York State Cab. Nat. 

 Hist., ISGl, p. 55, pi. 7, fig. 1.— Hall, Geol. Surv. Canada. Decade 2, 1S65, 

 p. 12, fig. 10; 20tli Rep. New York State Cab. Hist., 1868, p. 178, text 

 fig. 11 (rev. ed., 1868, 1870, p. 210, text fig. 11).— Nicholson, Mon. 

 Brit. Graptolitidfe, 1872, p. 129, text fig. 69. 



Dictyoncma rctifonne Spencer, Can. Nat, X, 1882, p. 165; Trans. Acad. 

 Sci. St. Louis, IV, 1884, p. 573, pi. 3, figs. 1, 2 ; Bull. Mus. Univ. State 

 Missouri, I, 1884, p. 23, pi. 3, figs. 1, 2.— Miller, Nortb Amer. Geol. and 

 Pal., 1889, p. 185, text fig. 168.— Pocta, Syst. Sil. Centre Bobeme, VIII, 

 1894, p. 192.— Gurley, Journ. Geol., IV, 1896, pp. 96, 308.— Roemer and 

 Frech, Letb. geog., I Tb., Letb. Pal., I, 3 Lief., 1897, p. 575, text fig. 

 145.— Grabau, Bull. New York State Mus., IX, 1901, pp. 133, 134, text 

 fig. 27; Bull. Buffalo Soc. Nat. Sci., VII, 1901, p. 133, text fig. 27.— 

 RUEDEMANN, New York State Mus., Mem. 11, 1908, p. 155, text fig. 64. 



This fine species, the genotype of Dictyonema, is a well-known 

 although rather rare form in the Niagaran (Rochester) shale of 

 New York. In Canada the species is confined to the earthy dolomites 

 and shales beneath the chert bed of the more typical dolomites. 

 Doctor Gurley has prepared the following redescription. based upon 

 the types and other specimens studied In' him : 



Polypary ratber strongly radiate, witb tbe brancbes usually about 0.8 mm. 

 wide (a few as narrow as 0.6 mm., a few swelling out to 1 mm., particularly 

 immediately below a bifurcation) ; about 15-17 in 25 mm. of widtb in tbe basal 

 portion, and in young specimens frequently somewbat more slender, more tor- 

 tuous (witb sligbt tendency to zigzag) and somewbat fartber apart; tbe inter- 

 si)aces consequently as wide as, or sligbtly wider tban, tbe brancbes. Dissepi- 

 ments mostly transverse (some are sligbtly oblique, a few very oblique) ; 

 generally slender (alwut 0.2 mm.), but a few reacb 0.3 mm., or rarely 0.4 nini. 

 Mesbes mostly oblong; a number of careful measurements bas sbown me tbat 

 tbe most usual (tbe typical) lengtb is on tbe average 1.5 mm. (between 1 and 

 2 mm.), but longer ones are seen, from covering up or destruction of tbe inter- 

 vening dissepiments, wbicb condition in favorable cases can be proven. Rarely 

 two successive dissepiments are not fartber apart tban 0.5 mm. Tbis almost 

 invariably results from tbe two dissepiments diverging from a common point of 

 origin on one brancb. 



