PISCES 



171 



ORDER III. ANASPIDA 



This order is established to contain two genera of fish-like forms, 

 Birkenea (Fig. 99, D) and Lasanius (Fig. 99, E) about which there is 

 only fragmentary information, and which are placed among the Ostra- 

 codermi only provisionally till more knowledge of their characters is 

 forthcoming. 



ANTIARCHI 



This group, placed originally among the Ostracodermi, is now given 

 class value and separated from the latter. It is from such forms as 

 Bothriolepis (Fig. 99, A) that Patten would derive the vertebrates 

 through the connecting link of the extinct sea-scorpions. Like the 

 Ostracodermi, the Antiarchi have a heavily armored carapace and a 

 free fish-like tail. The carapace is, however, differentiated into a 

 head-shield and a thoracic shield. According to Patten this creature, 

 which is fish-like in most of its characters, has the lateral paired jaws 

 of the Arthropoda and has a brain more arthropodan than chor- 

 date. Perhaps the most characteristic feature of the group is the pair 

 of appendages that is jointed to the cephalic carapace and reminds 

 one at the same time of arthropodan appendages and of vertebrate 



FIG. 100. Coccosteus decipiens. Side view, restored. A, articulation of head 

 with trunk; DB, cartilaginous basals of dorsal fin; DR, cartilaginous radials of 

 dorsal fin; H, haemal arch and spine; MC, Mucous canals; N, neural arch and 

 spine; V, median unpaired plate (?) of hinder ventral region; VB, basals of pelvic 

 fin; VR, radials of pelvic fin. (From Dean, after Smith- Woodward.) 



limbs. A lateral-line system of chordate type is quite clearly shown. 

 It has been suggested that the paired appendages may be the fore- 

 runners of the vertebrate jaws. This, however, seems rather far- 

 fetched. 



As has been previously stated this group is not only a highly special- 

 ized one, but, in its heavily armed body and evidently sluggish habits, 



