32 



The Ottawa Naturalist 



[May 



The true Phacopinid characters appear in the 

 Silurian. There takes place, as Reed (1905, 

 p. 176) has shown, a partial loss of pentamerism, a 

 shortening and broadening anteriorly of the glabella, 

 so that it is no longer high with subparallel sides, but 

 wide with markedly diverging lateral borders. The 

 third pair of side glabella lobes become greatly 

 reduced and are often nodular at the extremity. 

 There is a general absence of spines, the genal angles 

 being rounded off and the pygidium nonmucronate 

 with few segments. In addition to the smaller eyed 

 T rimer ocephalus forms, these modifications take 

 place in two distinct, though closely related, Silurian 

 groups, the one characteristic of the Tethys 

 (Bohemia) realm, and the other widely spread, but 

 typical of the northern Atlantic realm. For the 

 present, the former may be referred to as the group 

 of P. glockeri Barrande and the latter as the group 

 of P. stolfesii (Milne-Edwards). In the P. glockeri 

 group the anterior glabella furrows are broadened 

 and deepened in a characteristic manner, so that 

 the frontal lobe is almost detached as in Dalmanites. 

 The segregation of this group was recognized by 

 Wedekind (1911) who incorporated it under the 

 name of his genus G/oc^ena. It will be shown, 

 however, that this name cannot stand. In the other 

 group, apparently not represented in the Tethys 

 (Bohemia) realm the first and second pairs of 

 glabella lobes are almost completely fused with the 

 frontal lobe leaving only faint furrows, while the 

 third pair is profoundly reduced and at its ex- 

 tremities becomes characteristically nodular. In the 

 earlier Silurian this group includes Phacops orestes 

 Billings, Trilobites elegans Sars and Boeck and 

 Phacops (Portlockia) mar}(landemis, n. sp. In the 

 later Silurian it embraces Calymene stokesii Milne- 

 Edv/ards. While the group of P. glockeri becomes 

 extinct at the end of the Silurian, the second group 

 gives rise to numerous forms in the Devonian. But 

 as already noted by Wedekind (191 I) the Silurian 

 forms are considerably unlike their descendants. 

 They differ in their smaller size, poorer development 

 of tuberculose surface, especially of the glabella, 

 and much more depressed, never overhanging 

 anterior surface of the glabella. The last character 

 is very diagnostic and of stratigraphic value. 



SYSTEMATIC RELATIONS. 



Phylum Arthropoda. 



Class Crustacea. 



Subclass Trilobita Walsh. 



Order PropariA Beecher. 



Family Phacopidae Corda. 



Subfamily DalmaniTINAE Reed. 



Genus Dalmanitina Reed. 



1843. 

 1845. 

 1852. 

 1852. 

 1864. 

 1905. 

 1905. 

 1906. 

 1913. 

 1913. 



Acaste Goldfuss (non Leach) (partim), 

 Neues Jahr. Min., etc., 1843, p. 563. 

 Dalmania Emmrich (non Desvoidy) (par- 

 tim), Neues Jahr. Min., etc., 1845, p. 40. 

 Dalmania Barrande (partim), Syst. Sil. du 

 Centre Boheme, 1, p. 528. 



Dalmanites Barrande (partim), Syst. Sil. du 

 Centre Boheme, 1 , p. 934. 



Acaste Salter, Mon. Brit. TriL, Pal. Soc, 

 1864, p. 14. 



Geol. Mag., (5), 2, 



Reed, 



(partim), Geol. Mag., 

 Tril. 



Dalmanitina 



p. 224. 



Phacopidella Reed 



(5), 2, p. 173. 



Phacopidella Reed, Lower Pal 



Girvan, III, Pal. Soc, p. 156. 



Dalmanitina Raymond, Zittel - Eastman 



Textb. Pal., 2nd ed., p. 726. 



Phacopidella Raymond (partim), Zittel- 



Eastman Textb. Pa!., 2nd ed., fig. 1409. 



The genus Dalmanitina, proposed by its author 

 (as a subgenus of Dalmanites Barrande) for the 

 primitive generalized Ordovician types, is now ex- 

 tended to include what are here interpreted as sim- 

 ilar generalized forms in the Silurian. The generic 

 characters are: well-marked pentamerism of the 

 glabella without semi-detachment of the frontal 

 Icbe, genal angles rounded off or only produced into 

 short spines, pygidium with few segments and 

 rounded posteriorly or rarely produced in a short 

 mucronaticn. It includes Dalmania socialis 

 Barrande, Calymene doxvningiae Murchison, Pha- 

 cops (Acaste) consiricia Salter, and Dalmanitina 

 logani var. conservatrixe, n. var. The Ordovician 

 P. apiculata (Salter) apparently also belongs here. 



As here interpreted Dalmanitina is considered to 

 replace Acaste Goldfuss and in particular Salter's 

 use of it. Acaste was erected by Goldfuss in 1843 

 for forms with the pentamerism of the glabella re- 

 tained. It thus included forms now referred to 

 Dalmanitina, but of course was given a broader 

 interpretation than is now proposed for the latter 

 genus. Salter's use of Acaste was more restricted 

 and practically coincides with that of Dalmanitina 

 as here emended. Under it he places all the Silur- 

 ian forms listed above with the exception of the 

 then unknown Arisaig variety. Salter gave Acaste 

 only subgeneric rank, under the genus Phacops. 



Reed includes the Silurian forms now referred to 

 Dalmanitina in his broad subgenus Phacopidella, for 

 he did not extend the scope of Dalmanitina beyond 

 the Ordovician. He designated the Acaste forms 

 as falling within it and in 1906 referred Calymene 

 dorvningiae Miirchison to the subgenus (of Phacops) 

 Phacopidella. 



