1913] The Ottawa Naturalist. 29 



Speaking principally of T. fimbriatus, which is the better known 

 species, it has glabellar furrows, though not so well developed 

 as in the typical Tretaspis, but, so far as I can learn, lacks the 

 simple eyes and eye-lines of that genus. But the greatest 

 obvious peculiarity of the species is the character of the fringe, 

 which, instead of being marked by concentric rows of perfora- 

 tions, is crossed by a system of radiating ridges and furrows. 

 Reed has recently studied the fringes of the various English 

 species of " Trinucleus", and he speaks thus of the fringe in 

 Trinucleus fimbriatus-} 2 "The upper surface has all the pits 

 arranged in radial sulci except near the genal angles." And 

 again; "the dividing radial ridges vary from the extreme de- 

 velopment in T. fimbriatus, Murchison, to the scarcely differ- 

 entiated structures in T. nicholsoni." I am aware that Reed 

 also says of the arrangement of the pits in concentric or radial 

 rows that " Frequently different stages occur in the same species 

 or different parts of the fringe of the same individual, " and that 

 he does not seem to give very high classificatory value to the 

 pattern of the fringe. Still, we have here an extreme develop- 

 ment along one line, which, taken with the other characteristics 

 of the specimens, form a combination which may have the value 

 of a generic group. The principal characters seem to be as 

 follows: Glabella obovate, glabellar furrows present, but weaker 

 than in Tretaspis, eye-lines and simple. eyes absent in the adult, 

 fringe ornamented with radiating furrows separated by strong 

 ridges. I would therefore propose to select Murchison's second 

 species, Trinucleus fimbriatus, as the type of Trinucleus, and let 

 the genus stand or fall on the basis of that species. Ruedemann's 

 Tretaspis diademata would certainly belong to the genus as 

 thus restricted, and probably Trinucleus coscinorhinus , Angelin 11 , 

 as well. Professor F. R. Cowper Reed has announced his in- 

 tention of revising the British species of Trinucleus, and it will 

 be interesting to see if, when the species are better known, such 

 a grouping will be of value. We seem to have four possible 

 courses open to us, and of them I personally prefer the fourth : 



First, use Cryptolithus and make Trinucleus a direct 

 synonym. 



Second, ignore Cryptolithus and continue to use Trinucleus 

 on the score of convenience. 



Third, make Trinucleus fimbriatus the type of the genus and 

 make a broad enough definition to include the type of Tretaspis, 

 in which case Trinucleus would replace Tretaspis, the latter 



12 Geological Magazine, vol. 9, Dec. S, pp. 349, 385 .1912, 

 ln Bull. N. Y. State Museum, No. 49, p. 46, pi. 3, figs. 12-14,1901. 

 14 Pal. Scandinavia, vol. 1, 3d ed., 1878, p. 65, pi. 34, fig. 4. 



