NOTES ON PALEOZOIC CRUSTACEANS 85 



the preabdomen and postabdomen with the left lateral portion 

 •of the head-shield indistinctly retained^. The figure given by 

 -the author was reproduced by Eichwald (Lethaea 7^ossica. 1860. 

 p. 1445); and a restoration of the cephalic parts of the animal, 

 based on Nies^kowski's figure, but incorrect in the restored de- 

 tails, was given by Woodward^, and has found its way into 

 various works of more general character [see e. g. Packard's 

 Monograph of the North American phyUopod crustaoea). The 

 distinguished author of the genus believed that he detected 

 evidences of lateral compound eyes and suggested their presence. 

 Woodward, restoring the missing parts and accepting the sug- 

 gestion of ^^Tieszkoweki, represented it with large Limulus eyes. 

 When Schmidt redescribed the species in the work cited, having 

 an additional specimen of the head-shield, he pronounced against 

 the existence of these external organs, and our well preserved 

 specimens corroborate this determination fully. The animal had 

 no compound eyes, nor, so far as can be seen, ocelli; and, finding 

 no trace of any structure, spot or streak, which can be interpreted 

 as evidence of an optical organ, we are disposed to believe that 

 through degeneration Pseudoniscus had become sightless. 

 Associated with Pseudoniscus aculeatus in the 

 Eurypterus beds of Oesel are, besides Eurypterus 

 f i s c h e r i Eichw. and Pterygotus osiliensis Schmidt, 

 species of the allied genus B u n o d e s , three of which have 

 been recorded, B. lunula Eichw., B. rugosus and B. 

 schrencki Nieszk. The last of these was called by Niesz- 

 kowski Exapinurus schrencki; but both genus and 

 species were based on a highly imperfect specimen, and Schmidt 

 is unquestionably correct in regarding Exapinurus as a 

 synonym for B u n o d e s and the species as a probable variety 

 of B. lunula. There are between these genera Bunodes 

 and Pseudoniscus, similarities of structure which justify 

 their being placed together with Hemiaspis in the family 



^Schmidt Die Crustacean-fauna der Eurypterus-schichten von Rootzi- 

 kiill auf Oesel, p. 40; Mem. de I'acad. imper. des sciences. 1883. ser. 7, 

 V. 31, no. 5. 



^Palaeontogr. soc. Merostomata, 4:177, fig. 65. 



