PROETUS. DECHENELLA. 27 



Several kindred species are found in the Devonian Rocks of America, and one, 

 P. folliceps, 1 is even more like it than are its Continental analogues. Nevertheless 

 this differs in being very smooth, in having the cheek more raised and furrowed, 

 the eye smaller and more elongate, and the tail and border of the head smooth ; 

 while it agrees in having the cheek-angle rounded, without the trace of a cheek- 

 spine. P. macrocephalus, Hall, 2 has a distinct side-lobe to the glabella, long 

 cheek-spines, and more segments and a stronger border in the pygidium; and 

 P. crassimarginatus* Hall, has a more prominent and excavated border, a more 

 furrowed cheek, and more segments in the tail ; and it is smooth. 



Upon the whole, though P. audax nearly approaches several foreign species, I 

 am inclined to regard it as distinct from all of them. There seems some variability 

 in the width of the glabella, and further evidence will be required before several 

 of the characters can be regarded as established. Although several small German 

 specimens in the British Museum are very like it, their narrow, arched, smooth 

 neck-lobes, obsolete nodules and deep processes on the cheek, tuberculated 

 pygidia, and peculiar little cheek-spines seem enough to prove them to have 

 nothing to do with our present species. 



3. Genus. — Dechenella, Kayser, 1880. 



This genus was established by Prof. Kayser* for species of Phillipsia occurring 

 in the Devonian formation, and having tails similar to those of that genus, 

 but distinguished by their small, triangular, and deeply-furrowed glabella?. 

 He included in it three species from Germany and two from North America, 

 which had been formerly variously referred to the genera iEonia, Gerastus, 

 Proetus, and Phillipsia. 



1. Dechenella setosa. PI. II, figs. 15 — 17. 



1889. Dechenella setosa, Whidb. Geol. Mag., dec. 3, vol. vi, p. 29. 



Description. — Head rather flat, semi-oval, with straight cheek-spines. Border 

 flat, broad in front, bounded by a shallow concavity which becomes linear in 

 front. Central parts of head moderately convex. Glabella arched in profile, 

 somewhat flattened laterally, very triangular in outline, reaching almost to the 



1 1888, Hall, ' Pal. N. Y.,' vol. vii, p. 101, pi. xxiii, figs. 3—8. 



2 Ibid., p. 116, pi. xxi, figs. 10 — 21, and pi. xxiii, figs. 30, 31. 



3 Ibid., p. 99, pi. xx, figs. 6—8, and 20—31 ; pi. xxii, figs. 20—26, and pi. xxv, fig. 8. 



4 1880, Kavser, ' Zeitsch. Deutsch. geol. Gesell.,' vol. xxxii, p. 703, pi. xxvii. 



