Observations on the genus Eastrites and some allied species of Monograptus. 



21 



Monograptus gemmatus Barrande. 

 Pl. III, figs. 24—31. 



1850 Eastrites gemmatus Barrande, Graptolites de Bohême, p. 68, Pl. 4, fig. 5. 

 1863 cfr. Monograptus gemmatus Richter, Thüringische Graptolithen ; Zeitschr. d. 



Deutsch. Geolog. Gesellsch. Bd 5; p. 462, Tat XII, 



fig. 34. 



1897 Rastrites gemmatus Frech, Lethsea Geognostica I, p. 266, fig. 219: 6. 

 1897 Monograptus gemmatus Perner, Etudes sur les Graptol. de Bohème, p. 23, fig. 



26, Pl. 11, fig. 33. 



1899 Rastrites gemmatus Eisel, Ueher die Zoueufolge d. ostthüring. u. Vogtland. 



Graptolithenschiefer, p. 6. 



Barrande described this graptolite as a Rastrites, and, strange to say, Rich- 

 ter regarded the isolation of thecse more completely realized in this species than 

 in any other. As Perner has clearly demonstrated, however, it is a true Mono- 

 graptus, in fact, not even nearly related to any Rastrites. As only imperfect frag- 

 ments have heretofore been described and figured, I now give a more complete 

 characteristic of the species. 



The rhabdosome reaches an extent of more than 40 mm., and is very slender 

 throughout; when converted iuto pyrites it augments in width from .2 mm. near 

 the sicular end to .5 mm. in the distal part, but in compressed state it is almost 

 twice as broad. A specimen showing its most normal appearance commences with 

 a broadly arcuate portion emitting thecœ from the convex side, then bends in the 

 opposite direction, and graduates into a curve tending to form a centripetal spiral, 

 and carrying thecre on its inner edge. But on account of accidental fractures and 

 torsions, due to the tenuity of the rhabdosome, the specimens often exhibit an 

 aspect more or less deviating from that described above. In the distal portion the 

 thecse number from 8 to 10 in 10 mm., but in the earlier region, only 6 or 7 to 

 the same length. They are adpressed to the common canal, and widen almost im- 

 perceptibly upwards until they terminate in projecting narrow tubes, which are 

 reflexed and enrolled so as to form rounded knobs. In specimens preserved in 

 relief their apices seem to be turned to the one side, as seen in fig. 31, in which 

 drawing the very apertures are concealed by the visible part of the lobes. The 

 thecse are identical in form along the entire rhabdosome, but in the earlier half 

 of flattened specimens they commonly appear in the form of small reflexed hooks, 

 like those represented on Pl. Ill, fig. 30 of this paper, and in Perner's work on 

 pag. 23, fig. 26, and Pl. II, fig. 33. 



Localities and horizon. Sweden: in the year 1899, I found, in the 

 zone of Monograptus discus of Kinnekulle, some specimens of this species, con- 

 verted into pyrites. Thuringia: from Mr Eisel I have received excellent com- 

 pressed specimens, produced from the zone of Monograptus exiguus (zone 15) at 

 Paitzdorf and Loitzsch. Bohemia: At Li to hl aw I have collected both distal 



