AST. 11 SOME BUEGESS SHALE FOSSILS HUTCHINSON d 



the younger stages are represented by media which may for the 

 present be treated as the young of the former species. Of regalis 

 Walcott had four specimens of supposed males and two " females." 

 The latter, as indicated below, are probably not rightly referred to 

 Opahinia. I have examined eight specimens of 0. regalis in which 

 the head is sufficiently preserved to show the frontal process, two 

 in which it is well preserved but apparently lacks the process, and 

 numerous fragments. 



OPABINIA REGALIS Walcott 



Opahinia regalis Walcott, 1912, Smiths, Misc. Coll., vol. 57, p. 167. 

 Opahinia ? media Walcott, 1912, Smiths. Misc. Coll., vol. 57, p. 170. 



Head. — The most complete indication of the structure of the head 

 is given by the two specimens U.S.N.M. 57683 and 57684, figured 

 by Walcott, by a dorso-ventrally compressed specimen figured here 

 from a retouched photograph left by Walcott (pi. 1, fig. 4) , and by 

 a dorso-ventrally compressed specimen very similar to specimen 

 57683. All the sjDecimens are represented by both sides of the split 

 pieces of shale in which they are fossilized. The most conspicuous 

 feature of the head is the large frontal process which is visible in all 

 these specimens and in four other much less perfect ones. It con- 

 sists of an elongate cylindrical process, inserted on the extreme front 

 of the head, in the unfigured laterally compressed specimen it is bent 

 round at the side of the head covering the ventral part of the latter ; 

 in specimen 67683 it is flexed upwards, while in the two dorso- 

 ventrally compressed specimens it is shown squeezed out straight 

 forward. In none of these positions is there any sign of breakage 

 so that the process was certainly flexible. In the specimen figured 

 from Walcott's photograph in Plate 1, Figure 4, traces of an inter- 

 nal cavity can be made out so that it was probably erectile, being 

 filled with fluid as is the process of Thamnoce'phalus (Evans, 1915). 

 In the laterally compressed specimen 57683 the process, though hard 

 to measure on account of its flexure, is clearly less erected than in 

 either dorso-ventrally compressed specimens. Anteriorly the process 

 is dilated in the two latter specimens and is distinctly cleft apically. 

 The extreme tip bears a number of large spinous projections. The 

 whole surface of the process is somewhat wrinkled and the apical part 

 apparently bears some very small spines arranged in irregular rings. 

 Well preserved compound eyes are found on the dorso-ventrally com- 

 pressed specimens. In the individual figured on Plate 1, Figure 4 the 

 large dark ommatidial part is particularly clear. The ocular pe- 

 duncle appears to have been very similar to that of modern Anostraca. 

 In the laterally compressed specimen 57683 the eyes, though much 

 broken, can also be made out, the stalks on which the}^ are set being 

 directly dorsally. No appendages could be found on the head by 

 Walcott. 



