20 



Sv. Leonh. Törnquist. 



one another. The confusion can, however, be accounted for by the circumstance 

 that examples of Monograptus convolutus are occasionally met with in which not 

 only the proximal thecse, but also those of the exterior volutions appear to be 

 isolated. So far as I have observed, this appearance depends upon the mode in 

 which the fossil has been preserved in the rock. I have collected specimens of 

 this kind both in Östergötland and in Dalarne, always lying in seams or spheroidal 

 concretions of calcareous shales, and preserved in half relief (See Figs. 22, 23)- 

 The apparently isolated thecse, which are sometimes mingled with others of normal 

 shape, are partly concealed by the matrix, and may by means of an awl or a 

 needle be prepared out so as to display their regular form. If I am not mistaken, 

 Hisinger's originals occur in shales of that description. 



As already mentioned (p. 12), Carruthers in his paper »A Revision of the 

 British Graptolites», has (Pl. V, fig. 1 a) reproduced a very perfect but rather 

 enigmatic specimen of Monograptus convolutus, the earliest theca? of which are un- 

 commonly long; and in the accompanying description the author states that these 

 thecse show indications of having been provided with such terminal bristles as are 

 seen in the thecse illustrated in his figs 1 b and 1 c. After examining the original 

 of Carruther's fig. 1 a, Lapwortii says that he is inclined to believe that its 

 strange appearance is » owing to the accidental juxtaposition of two different forms». 

 Such an interpretation of Carruthers' drawing has also appeared to me most 

 plausible; and when, many years ago, I was examining the collection of British 

 graptolites sent by Professor Lap worth, already referred to, and then found a slab 

 from Craig Mich an Scaurs containing Monograptus convolutus associated with 

 short fragments quite agreeing with Carruthers' figs 1 b and 1 c, I did not 

 hesitate to identify the latter with Rastrites phleoides, which species I was just going 

 to describe 1 ). I was, accordingly, not a little surprised when lately, in a collection 

 of graptolites from «Colonie Haidinger» made by myself in 1889, I came 

 across one specimen in many respects resembling Carruthers' fig. 1 a. Not only 

 were the proximal thecse uncommonly long and apically emarginated, like those 

 of Rastrites rastrum Richt., but I even thought that 1 could detect at. the 

 very apices traces of bristles. Unfortunately this part of the rhabdosome was 

 destroyed while I was trying to prepare it better for delineation. I dare draw no 

 conclusion from this single observation, so much the less as my previous descrip- 

 tions of Monograptus convolutus were based on specimens which admit of no mis- 

 interpretation, but I have thought the fact mentioned deserve not to be left un- 

 noticed. 



') Törnquist, Anteckningar om de äldre paleozoiska leden i Ostthüringen och Voigtland; 

 Geol. Fören. i Stockholm Förhandl.; Bd IX; 1897, p. 490. 



