Dr. Herrmann — On Dichograptidce — a Family of Graptolites. 13 



Y. — On the Graptolite Family Dichograptid^, Lapw. 



By Dr. Otto Herrmann. 1 

 [Translated and Abridged by W. S. Dallas, F.L.S.] 



Sub-order Khabdophora, Allm. Group Graptolitid^, Lapw. 

 Family Dichograptid^, Lapw. 



Hydrosoma bilaterally developed. Branches regular, always fur- 

 nished only with a single series of hydrothecse (Monoprionidian). 

 Hydrothecas rectangular, touching one another, their inferior margin 

 slightly curved. Sicula generally persistent ; its free, pointed, down- 

 wardly directed end at the proximal extremity of the hydrosoma. 



In 1851 M'Coy (Brit. Pal. Foss. p. 9) proposed the generic name 

 Didymogr aptus for two-branched species with one row of cells 

 " sometimes on the inner, sometimes on the outer side of the 

 branches." Nearly at the same time Geinitz established his genus 

 Cladogr-aptus to include all two-armed or furcate Graptolites. These 

 two denominations have been employed in various senses by succeed- 

 ing authors, and considerable confusion has resulted. Hall 2 remarked 

 that these genera contained at least two distinct types, and proposed 

 to retain the name Didymogr aptus for such forms as D. MurcJiisoni, 

 Beck, and to give that of Cladograptus to Didym. divaricatus, Hall, 

 and its allies. His genus Dicranogr aptus applied to forms like D. 

 ramosus, Hall, may be dropped. 



In 1871 Hopkinson 3 separated such forms as Didymogr 'aptus 

 (Cladogr.) Forchltammeri under the generic name of Dicellograptus. 

 He adopted Hall's view of the nature of Didymogr aptus, abolished the 

 name Cladograptus as a designation of two-branched Graptolites, and 

 accepted Hall's name Dicranogr aptus. The two-branched Graptolites 

 were thus divided into three genera : — 



12 3 



Fig. 1. Diclymograptus vacillans, Tullberg. 

 ,, 2. Dicellograptus Forchhammeri, Geinitz. 

 ,, 3. Dicranograptus ramosus, Hall. 



1 Abridged from the third chapter of Dr. Herrmann's paper in the Nyt Magazin 

 for Naturvidenskaberne, vol. xxix. pp. 124 — 214. (See also Geol. Mag. 1885, Dec. 

 III. Vol. II. pp. 406 and 448.) 



2 Introduction to the Study of the Graptolites, Albany, 1868, p. 234. 



3 Geol. Mag. 1871, Vol. VIII. p. 20, PL I. 



