cxxxii BRITISH GRAPTOLITES. 



He gives special attention to the structure of the proximal 



1xr . end and shows how the first thecas originate from the disk of 



Wiman, & 



" XJeber Bictyonema attachment (" haftscheibe "). 



camrnommr ' Bull. By means of cross sections he finds that two individuals 



Geol. lust. Upsala,' f different sizes appear to arise from the disc of attach- 

 ment, and he gives various explanations as to their origin. 

 He inclines to the view that the larger individual was the older and was 

 originally free-swimming, and that from it the smaller budding individual was 

 developed. Another explanation which he considers probable is, that both thecas 

 were produced from an older and non-chitinous individual which was originally 

 free-swimming. 



1897. 

 Tornquist, In 1897 Tornquist published the first part of his Mono- 



" On the Diplograptidse grapn on « The G- rap t lites of the Rastrites Beds." In this 



and the Heteroprionidse i ■% , -.i ii t-v i ^- n -\ ^i tt ^ • -i 



c ,, ~ • „ , ., he deals with the Diplograptidae and the Heteropriomdas, 

 or the bcanian Rastrites r o x i 



Beds," ' Acta Reo-. Soc. anc ^ describes and figures several species of Biplograptus and 

 Physiog. Lund.,' vol. Glimacograptus, some of which are new to science. 



vm. 



Description of Species. — The descriptions and illustrations are excellent, and 

 are specially concerned with the elucidation of the detailed structure of the 

 proximal end, which had previously remained almost unnoticed. The species 

 described include the well-known forms : Glimacograptus scalaris, G. rectangitlaris, 

 G. undulatvs, Biplograptus palmrus, B. folium, I). acuminatus, D. cometa, D. 

 tamariscus, D. bellulus, D. longissimus, and in addition two new species : Glimacog. 

 medius and Diplog. cyperoides, and a new varietal form, Dimorphog . Swanstoni 

 var. Kurcki. 



Tornquist considers that " at present it is advisable to retain the genus Diplo- 

 graptus undivided," and he therefore does not adopt the sub-generic names of 

 Pelalograptus and Gephalograptus. 



Terminology. — Tornquist discusses various questions of terminology, and 

 endeavours to bring the nomenclature employed by Wiman, Holm and himself 

 into uniformity. He considers that the terms " obverse " and " reverse " aspects 

 are liable to less ambiguity than those of " sicula " and " anti-sicula " side, and he 

 also prefers the names "primary" and "secondary" to the "left" and "right" 

 for distinguishing between the two series of thecse. He proposes the term 

 " prolific side " for that side of the sicula which " communicates with the proximal 

 cavity of the rhabdosome." The opposite side he calls the " dorsal " side. 



He also suggests the new name " virgella " for the " so-called proximal 

 prolongation of the virgula." 



He discusses in some detail the question of the exact application of the words 

 " theca? " and "common canal," and thinks that the term " theca" is a convenient 



