68 LINDSTRÖM, VISUAL ORGANS OF THE TRILOBITES. 



tubercle. The cephalic eyes are lengthened prisras covered by a thick raerabrane. Thev 

 are convex at their base and in a transverse section they show a radiate structure of 

 their interiör. 



Proet. eonspersus Angelin. 



Pl. VI figs. 24—26. 



We have figured a deeorticated hypostoma vvith impressions of two reniforra maculse. 



The vertical sections of the cephalic eyes show a thin stratum where the lenses 

 are much shorter than in the previons species and covered by a thin film of the cominon 

 test. The same is also the case in a species which probably is Proet. verrncosus. 



Proet. signatus Lindström. 



Pl. VI figs. 27 — 30. 



On the lateral borders of the hypostoma there are short spines, two on each side, 

 but they are placed differently on the specimens and even wanting in some. The elong- 

 ated, elliptical maculse bear in their lower end a white spöt on which is seen a little 

 duster of a varying nnmber of small, segregated ocelli, from three to tive, according to 

 the different specimens, like so many black points. The maculre attain the exceptional 

 lengtlt of 4,7 millim. in some specimens, but commonly only 2 millim. We have as yet 

 not been able to detect these remarkable ocelli in any other species of Proetus. 



Ptychoparia (Oroa. 



Walcott in »Palseontology of the Eureka District», gives on plate X fig. 21 a re- 

 presentation of a hypostoma which near the posterior margin shows two maculaj as nar- 

 row, crescentlike ridges and above them two longer and thicker ridges directed obliqnely 

 toward the central axis of the hypostoma. 



Ptychopyge Ang. 



Previous figures of hypostomas with rnaculse are the following: 

 /'f. aciculata Br. II, pl. 1 iig. 13. 

 Pf. (jlabrata Br. II, pl. 1 fig. 14. 



Pt. aciculata Ang. 



Pl. VI figs. 40, 41 



The broad hypostoma bears the elongated, acuminated macnhe in an oblique diree- 

 tion, contrary to what is scen in inöst other species. r lTie antcrior end slopes inwards and 





