NO. 13 DIKELOCEPHALUS AND OTHER GENERA 365 



limitations now given the genus, it is restricted to the areas mentioned 

 above. It is quite probable that with more thorough collecting, it 

 will be found along the front range of the Rocky Alountains. 



It does not occur in the St. Lawrence Valley of Canada, but frag- 

 ments of what may be a species of the genus occur in the Champlain 

 Valley in Franklin County, northwestern Vermont, both in the Upper 

 Cambrian limestone (Locality 87) and the superjacent limestone 

 conglomerate (Locality 162). 



Diuiensions. — This genus includes the largest species of the Dikelo- 

 cephalinge. One cranidium has a length of 9 cm. and width of 9 cm. 

 at the palpebral lobes. If to this were added the proportional wide 

 free cheeks, the width of the cephalon at its posterior margin would 

 be 24 cm. A pygidium has a width of 18 cm. with length of 9.5 cm. 



A fragment of a large thoracic segment, preserving the pleural 

 lobe has a length of 18 cm. with a longitudinal width of 1.5 cm. 



On the basis of the above parts an entire trilobite of this genus evi- 

 dently existed 32 cm. in length with a width of 24 cm. 



Observations. — The earliest illustrations of the genotype of Dikelo- 

 ccphalus, D. minncsotensis, are on a plate accompanying a report by' 

 Dr. David Dale Owen, published in 1848.^ The plate faces page 58 

 of the report and the specimens are referred to the genus Asaphus. 

 These include the cranidium and pygidium of a large trilobite that 

 was in 1852 placed under the genus Dikelocephaius. 



Dr. Owen (1852) did not have any entire specimens, but from the 

 resemblance of fragments of Dikelocephaius to Ogygia he compared 

 the genus with the latter and thought it probable that the number of 

 thoracic segments was eight as in Ogygia. He described, illustrated, 

 and named five species, D. minnesoteiisis, D. pepinensis (=Saukia), 

 D. miniscaensis (=Ptychaspis), D. granulosus (=Ptychaspis), and 

 D. ioweiisis (=CrepicephalHs). 



Dr. E. Billings (1869) noted that he thought the doublure beneath 

 the head of Dikelocephaius was continuous and was not cut by the 

 facial suture. He referred several new species to the genus, D. niag- 

 niHcus {=^ Apatokephahis ff), D. planifrons (= Anomocare) , D. 

 belli {^^ Anomocarella), D. ozvcni {=^ Anomocare) , D. megalops 

 (:= Anomocarella f), D. cristatus (= Ptychaspis). 



Dr. James Hall reviewed the genus in 1863 and referred three new 

 species to it, D. spiniger (=^ Saukia), D. inisa (= Conokephalina), 

 D. osceola (= Osceolia), and illustrated them from fragmentary 



^ Report of a Geological Reconnaissance of the Chippewa Land District of 

 Wisconsin, etc. Senate Doc. Exec. No. 57, 30th Congress, ist Session, 1848, 

 p. 15, pi. 7, figs. 2, 3. 



