LASIOGRAPTUS. 319 



When they take the form of spines they are, unlike those in the Glossograpti, 

 always more or less flexed, and often become distinctly fibrous. These spines 

 appear to be always ventral in origin, septal spines or spurs like those in 

 Glossograptus being unknown in the Lasiograpti. But in place of the septal 

 spurs, however, there occur in two sub-genera of this group remarkable septal 

 processes (scojmlss, Hopkinson and Lap worth, 1875), each consisting of a pair of 

 fairly stout stem-like fibres, which give off or break up into branches and fibrillae, 

 supporting a membranous film that usually shades away at its extremity into the 

 surrounding rock. These scopulse appear to be identical with the " reproductive 

 processes " of Hall (Gr. \_Orthog.~\ Whiffieldi). Sometimes the scopulas present the 

 appearance of a double membrane, web, or sac, outlined along its lower and 

 upper edges by a strong fibre originating as an unbranched filiform process. 

 Sometimes these septal processes with their sac-like membranes are seen to arise 

 directly from the naked central strand well beyond the distal extremity of the 

 polypary (Fig. 212 ft). 



The ventral processes in the Lasiograpti are typically mesial in origin, though 

 in some forms there may apparently be apertural processes in addition. In all 

 cases they seem to be paired, and in many cases to be formed, as it were, of the 

 naked prolongations of the fibrous thickening of the angles of the thecal walls 

 etc., the thickening extending continuously backwards to the central line or to 

 one of the septal strands of the polypary. When these ventral processes take 

 the form of spines they may be free (Haling, mucronatus), or each pair may 

 support between them a fan-like or tongue-like membrane or pelta (ffallog. 

 var. bhuucronafus). When the ventral processes take the form of filaments or 

 fibres, these are in some cases free and almost straight (Thysanog. retusus). 

 Generally, however, these filamentous processes are bent into a graceful declining 

 curve (usually convex outwards) and eventually unite with the corresponding 

 filaments of the processes immediately below, giving origin in this way to a 

 complete marginal lace- work of fine filaments, which extends continuously along 

 the whole ventral side of the polypary. This ventral lace-work varies much in its 

 details ; sometimes it is fairly simple, and is formed throughout of two pairs of 

 sub-parallel filaments united by cross-threads (Thysanog. Harhiessi); sometimes 

 the filaments break up again and again to form a finer lace-work (Neurog. fibratus) ; 

 and in one sub-genus (Nympkograptus) the lace-work is still more complex, being 

 formed of long, sub-parallel strands united by fine cross-fibres, and apparently 

 forming a peripheral lace-work surrounding the whole of the polypary. For this 

 marginal lace-work we suggest the neutral term lacinia, leaving it to future 

 research to determine how much of it lies wholly extraneous to the ventral edges 

 of the thecae themselves. 



Within the limits of the genus Lasiograptus as at present understood there are 

 but few known species ; but these are so distinct in their external characteristics 



