ICI 6. No. I o. THE LOWER CAMBRIAN HOLMIA FAUNA. 8l 



gated. The medial spines of the segments, too, appears to have been 

 different. 



As regards the relationship of this form, I refer to the remarks in 

 the section dealing with this subject (page 71). 



Some General Remarks on the Structure and Development 



of the Meson acidae. 



I. The Obliterated Facial Sutures. 



As MoBERG 1 pointed out we see in Kjerulfia Lwidgreui Mob., and also 

 occasionally in Holmia Kjerulfi Lnrs., a fine raised line, that runs in an arc 

 from the posterior edge of the eye to the posterior margin in front of the 

 intergenal rib. This line could also clearly be seen in Kjerulfia lata. It 

 appears reasonable to assume with Moberg that this is a case of a re- 

 mainder of the obliterated facial suture. Moberg was probably also right 

 in giving the same interpretation to the remarkable lines that sometimes 

 are seen in both of the above genera running from the anteTior edge of 

 the eye to the marginal brim, in a markedly receding arc. If this repre- 

 sents the front branch of the facial suture, the latter would certainly have 

 a remarkable course, which it is true is also seen to some extent in cer- 

 tain genera of Paradoxidae, e. g. in Par. rugidosus Corda 2. 



Curiously enough, Walcott does not appear to have observed Mo- 

 berg's interesting discovery ^. The posterior part of the facial suture, 

 which Moberg drew attention to, is quite distinct from the line that 

 Walcott discovered on a specimen of Paedeumias transitans, the course 

 of which is such that it cannot be explained in a similar manner with any 

 degree of probability. 



II. Hypostome and Hypostome Attachments. 



As has long been known, the hypostome in Holmia is immoveably in- 

 serted in the remarkable portion of the shell on the under side of the 

 cranidium, which was first described by Holm^ and which Moberg^ termed 

 the hypostome attachment. The same condition is seen in Kjerulfia, the 

 hypostome attachment of which is unusually broad (Cf. text figure 13). 



1 Sveriges àlsta kända Trilobiter, pag. 323 og 354 (Geol. Föen. i Stockh. Förh. Bd. ar, 

 1899. 



2 See especially K. A. Grönwall, Bornholms Paradoxides lag, 1902, pl. 3, fig. 5. 



3 Olenelliis and other Genera of Mesonacidae, page 242 and pl. 33, flg. I. 

 ■* Om Olenelhts Kjerulfi, pag. 15. 



■5 Sveriges älsta kända Trilobiter, pag.324. In Swedish by Moberg termed „hypostomfästet". 



Vid.-Selsk. Skrifter. \. M.-N. Kl. 1916. No. 10. 6 



