ANASPIDA 



205 



known genus, Euphcmerops, from the Upper Devonian of Canada 

 (A. S. Woodward [503a]). They are fish-like in shape, with fusiform 

 body and heterocercal tail (Figs. 178, 

 179). The ventral lobe of the caudal 

 fin is well marked. They have hard 

 exoskeletal scales, the histological char- 

 acters of which are not thoroughly known, 

 and in which no bone -cells have been 

 found ; and both Birkenia and Lasanius 

 have a median ventral row of strong pro- 

 jecting scales. Birkenia and Euphcmerops 

 have a small median dorsal fin ; but in 

 none of the Anaspida is there any trace 

 of paired fins or flaps. 



The mouth appears to have been 

 ventral, below the rounded snout. Neither 

 nostrils nor orbits can be certainly identi- 

 fied, although a pair of rounded spaces in 

 Birkenia and two skeletal rings in Eupha- 

 nerops may possibly indicate the position 

 of the eyes on each side of the head. In 

 the former genus, also, is seen a row of 

 eight small holes set obliquely on each 

 side at the back of the head, which are 

 supposed to represent gill-openings, and 

 recall similar apertures in Tremataspis 

 (p. 204). The systematic position of the 

 Anaspida remains quite uncertain. The 

 heterocercal tail and the dorsal fin they 

 possess in common with other Ostra- 

 codermi ; in the disposition of the scales 

 on the trunk, and in the presence of a 

 row of branchial (?) openings, they approach 

 the Cephalaspidomorphi. 



Family Birkeniidae. Birkenia is com- 

 pletely covered with scales, small on the head, 

 larger on the trunk, and smaller again on 

 the caudal tin. On the body they are chiefly 

 set in regular oblique rows inclined forwards and downwards (Fig. 178). 

 The scales have a slightly tuberculated surface [466]. 



Birkenia, Traq. ; Silurian, Scotland. 



Family Lasaniidae. A single row of small scales followed by a set 

 of eight parallel oblique rods placed on either side behind the head, together 

 with a ventral row of very uniform recurved scutes, seem to represent all 

 that remains of the bony exoskeleton in Lasanius. Possibly the parallel 

 rods passed between gill-slits. There are indications of rays on the caudal 

 fin [466, 469]. 



