301 BRITISH GRAPTOLITES. 



Family GLOSSOGRAPTIDJE, Lapwortli. 



1873. Glossograptidii', Lapwortli, Geol. Mag., vol. x, tabic 1, p. 555. 



1880. Lasiograptidse, Lapwortli, Ann. Mag. Nat, Hist. [5], vol. v, p. 175. 



1880. Lasio<jraptid;v or Glossograptidae, Lapwortli, Ann. Mag. Nat. Hist. [5], vol. vi, p. 188. 



Biserial Graptoloidea with straight polyparies ; test membranous, continuous, 

 attenuated, more or less strengthened by lists, ribs, or filaments, which may, in 

 whole or in part, constitute together a supporting net-like framework or skeleton. 

 Thecce of the general Diplograptid type, provided with spurs, spines, or other 

 processes, which may be simple, branching, or connected to form an external 

 lacework of marginal meshes. 



A first and most characteristic feature of this family is afforded by the invariable 

 presence of external processes in the form of spurs, spines, or strong filaments. Some 

 of these agree in all essentials with those met with in the spine-bearing species of 

 the Diplograptidas (Ortlwg. quadrimucronatus, etc.), but others are very different, 

 and in no other family of the Graptolites are these processes so distinctive or so 

 varied in their form and peculiarities. 



These extraneous processes in the Glossograptidae are either medial or marginal 

 in position ; occurring either along (1) its central longitudinal line (/. e. that marked 

 by the sutural groove in those Diplograptidas which are provided with a septum) 

 or (2) its ventral edges. As the terms mesial and marginal are pre-occupied, 

 the two sets of processes are here classed as septal and ventral, these terms being 

 employed merely as indicative of relative position. 



The septal processes, when present, apparently arise at right angles to the axes 

 of the thecae, and form two ranks- — one on the obverse and one on the reverse 

 aspect. In both ranks they appear to be given off from the bases of alternate 

 thecae. 



The ventral processes are either apertural or mesial in origin with respect to 

 each theca, arising either from the angles of the apertural margin or from the 

 upper angle of the excavation. In both cases they always appear to be paired. 



Both septal and ventral processes may, within the limits of the family, take 

 the form of (1) rigid blind spurs (Fig. 205 e), (2) more or less flexuous spines 

 (Fig. 204), or (3) filamentous and fibrous processes, either simple, branching, or 

 anastomosing (Fig. 213 c). When in the form of simple spurs or spines they 

 significantly call to mind the proximal spines of the polypary in some of the 

 Diplograptidas, and, like those, occasionally support between them a membranous 

 pelta, web, disc, or vesicle (Fig. 212 b). The branching processes are usually more 

 fibrous in their nature and may support a much larger vesicle or pelta (Fig. 212 a). 



