132 Carruthers — On British Graptolites, 



misunderstood. It is a misfortune that cannot now be corrected, that this, the 

 only species which Linnaeus describes, finds a resting place in one of the most 

 recently established genera, instead of being the type of the genus Graptolithns. 

 Loc. Moffat, etc. 



2. C. mimitus, sp. nov. (PI. V. Fig. loa, b). This is a very minute but well- 

 marked species, never attaining a greater size than represented on the Plate. 

 There are at the rate of from 32 to 40 cells in the space of an inch. Loc. Moffat. 



3. C. bicornis. Hall (Grapt. Quebec, Gr. p. in). Loc. Moffat. 



4. C. biillatiis, — Diplograpsics bullatus^z\.\.. (Quart. Journ. vii., p. 174, pi. x., 

 fig. 2). Loc. Piedmont Glen. 



I have never seen a specimen oi D. pennatus^ Harkn. ; it probably belongs to 

 this genus, if it be not founded upon two mono-prionidian forms accidentally 

 placed back to back. 



Gen. X. DiCRANOGRAPTUs, Hall (Grapt. Quebec Gr. p. 57). Poly- 

 pary in the proximal portion, with a double series of cells, but di- 

 viding distally into two branches, with a single series of cells in their 

 outer aspect. Hall describes this genus as having the structure of 

 Climacograjptus, as regards the cells in which the polypites were 

 lodged, but in the two British species the polypites are certainly lodged 

 in true hydrothecas. The form of the polypary, however, supplies 

 sufficient characters for the separation of the group as a distinct 

 genus. 



Sp. I. D. ramosus. Hall (Grapt. Quebec, Gr., p. 57), Loc. Moffat. 



2. Z>. Clingani, sp. nov. (PI, V., Fig. 7 a, ^, c). Polypary with a short 

 diprionidian portion, the proximal end furnished with three very delicate spines ; 

 hydrothecae forming a slight serration along the margin ; 21 cells in the inch. 

 Loc. Moffat. 



Gen. XI. — Eetiolites, Barr. (Grapt. Boh., p. 68). Polypary 

 without a solid axis, cells arising from a central common canal in a 

 double series, and in contact throughout their whole length. Poly- 

 pary reticulated on the outer surface. 



In Dicranograptus the double septum and axis become separated in the branches 

 into their elements, forming a closed back and axis to the two mono-prionidian 

 polyparies. The structure of Diplograpsus is exactly that of the proximal portion of 

 Dicranograptus, being theoretically, if not actually, composed of two mono-prioni- 

 dian polyparies, united back to back. In Climacograptus the filiform axis alone re- 

 mains, and the divisions between the polypites is carried down to the axis, leaving, 

 however, a continuous free space on either side of the axis for the common coeno- 

 sarc. In Retiolites this union is still more complete, the ccenosarc of the colony 

 being common to the two series of polypites by the total disappearance of the 

 axis and dorsal portion of the epiderm in Graptolithus, or axis and septum in 

 Diplog7'apsus. 



Sp. I, R. Geinitzianus, Barr. (Grapt. Boh., p, 69). (Murch. Sil., Ed. IV., p. 

 541, fig. 2,) Loc, Cumberland. 



2. R. venosus. Hall (Pal. N. York ii., p. 40, pi. 17 A., fig. 2). Loc. Cum- 

 berland. 



Gen. Xn. — Phyllograptus, Hall (Canada Geol. Keport, 1857, 

 p. 135). Polypary consisting of four laminse of cells united rectan- 

 gularly by their longitudinal axes. 



The British specimens of this genus which I have seen exhibit only thin films 

 on the surfaces of highly indurated or somewhat metamorphosed rocks, sufficient 

 to determine their relation to Hall's genus, but utterly insufficient to exhibit any 

 details of the remarkable structure of the genus. If I rightly understand Hall's 

 descriptions and figures, the individual polypites in this genus are entirely separated 

 from each other, the septa between the hydrothecae being united [to the periderm 

 and continued to the axis. This structure is so anomalous among the GraptolitidcB 

 that I am inclined to think that I misunderstand it, especially as Hall does not 



