DENDROID GRAPTOLITES OF HAMILTON, ONTARIO. 



41 



Below is given Doctor Spencer's original description, with addi- 

 tional characters, as published by him in 1884, placed in brackets. 



Frond flabellatc. hut cyatbiforni in jurowing state; bifnrcatinj;; branches with 

 dichotomous terminations; [stem terminating in a well-marl^ed bulb] ; branches 

 (marlved with strije) more or less reticulated, and united, or overlaid bj' others. 



This genus is established on account of its bulbous root, which as yet has been 

 found in no other species of this family. The numerous branches closely overlie 

 each other or are connected in the form of a network without transverse dis- 

 sepiments, as in Dictyoncma. Fragments of these somewhat resemble species 

 of CaJyptograptiis, but have a much more [regularly] netted appearance and 

 the branches are much more delicate. 



Genotype. — Rhizograptus htdhosiis Spencer. 



RHIZOGRAPTUS BULBOSUS Spencer. 



Rhizograpsus bulbosiis Spencer, Canadian Nat.. VIII. 1878, p. 460. — Gtjelry, 

 Journ. Geo]., IV. 1896, pp. 101. 308. 



RMzograptus bulbosus Spencer. Trans. Acad. Sci. St. Louis, IV, 1884, p. 

 580, pi. 4, fig. 4; Bull. Mus. Univ. State Missouri, I, 1884, p. 30. pi. 4, 

 fig. 4.— Miller, North Amer. Geol. and Pal.. 1889, p. 202. text fig. 215. 



The original description is as follows: 



Frond cyathiform in growing state; numerous 

 bifurcating branches overlie each other, or are 

 united at points of contact to form a networl^, 

 with fine, more or less irregular, rhomboidal in- 

 terstices. The branches unite at base into .i 

 slender axis which terminates in a bulbous root. 

 The branches are usually less than one-fiftieth 

 of an inch wide, and in some specimens short 

 abrupt spinelike branchlets are given off. The 

 texture is corneous. Only a few specimens have 

 been obtained, except in fragments. Frond is 

 about 2 inches high. It was first found by 

 Colonel Grant in the Niagara limestones [near 

 the base of the " chert bed " at the " Jolly-cut " ; 

 1884] at Hamilton. Ontario. 



Doctor (xurlev's notes on this s})ecies arc 

 as follows: 



FlC. .52. RHlZOCiRAPTl S BCLBO- 



sus Spencer. The type-.spec- 

 IMEX. (After Spe.vceu.) 



The description of 1884 adds that the axis is athecaphorous; that the striie 

 along the branches (which vary in thickness from 0.25 to 0.33 mm.) appear 

 to mark the depressions of the common canal lietween the original positions of 

 the polypites; that the thecal apertures have an ellipsoid form, and there are 

 about 4 orifices in 1 mm. ; and that on the side of the branch opposite the 

 thecje is a " solid axis." 



After a careful examination of Rhizograptus bulbosus, in which the pseudo- 

 meshwork is well preserved, I can find no criteria to justify its generic dis- 

 tinction from the Calyptograptiis series, now that the basal " disk " has been 

 found in the latter. While I would provisionally recognize Rhizograptus as a 

 subgenus, I can not define it, and I think it probable that further study of large 

 collections will lead to its entire suppression. The only difference I can see is 

 a somewhat different aspect of the branches, which seem of a more rigid tex- 

 ture, more knotty and zigzag-flexuous than any of the Calyptograptus species. 



