210 THE DEVONIAN OF MISSOURI. * 



claw-like spine that is about 1/12 of total length of pygidium; elevated axially from 

 posterior extremity of axis into caudal spine. Axis consists of about 16 or 17 rounded 

 annulations, tapers regularly; its length about 4/5 that of entire pygidium, its width 

 at anterior end about 3/11 of width of pygidium, its width at posterior end about 

 1/3 that at anterior end. Each lateral lobe has 12 or 13 rounded ribs which are wider 

 than intervening furrows and marked with narrow, shallow, longitudinal groove. Sur- 

 face appears granulose under hand lens. 



Dimensions — Two of the specimens are of equal size, more nearly complete, and 

 slightly larger than the others. The two larger specimens : Length — inclusive of spine — 

 25.5 mm., width 32 mm., length of axis 20 mm., anterior width of axis 9 mm., length 

 of spine 2 mm., width of border 1.5 mm. 



Remarks — This pygidium is distinguished by the short, slightly upturned, claw-like 

 caudal spine. 



A number of parts of pygidia that are in all probability of this species cannot be 

 referred to it with certainty because in every case the posterior portion is broken off. 

 The range in size is indicated by the specimens figured. 



Genus Phacops Emmrich 



Phacops hudsonicus Hall 



Plate 56, figures 5-10 



Phacops hudsonicus Hall, 1859, Pal. N. Y., vol. Ill, p. 355, pi. LXXIII, figs. 24a, 26-28 



1861. 

 Phacops hudsonicus Girty, 1899, U. S. Geol. Surv., 19th Ann. Rept., pt. Ill, p. 571, pi. 



LXXI, figs. 4a-d. 



Description — "Head semi-elliptical; length greater than half the width; posterior 

 angles extended and abruptly rounded. Cheeks broad triangular, produced behind. 1 

 Glabella subpentagonal; length nearly one-third greater than the width. Frontal lobe 

 very prominent, gibbous above; middle and anterior transverse furrows distinctly 

 impressed in the cast; first annular furrow faintly defined; first annulation not promi- 

 nent, with two pustules at the summit and a node at each extremity; occipital furrow 

 and annulation strongly defined. Eyes small, extending backwards to the line of the 

 first annular furrow, having an elevation of four ranges of lenses. 



"[Remarks] — This species is founded on a single head (the test being removed 

 from the glabella), which is more produced in front than the P. logani; the eyes are 

 smaller, and not extending so far backwards." — Hall, 1859, 1861. 



"It is interesting to note that this species * * is quite plentiful in Indian 

 Territory, being more largely represented than the accompanying form, P. logani. 



* * The quantity of material examined makes it possible to add some details 

 to Hall's description which may be amended as follows: 



"Head semi-elliptical, varying somewhat in proportions but always transverse, 

 the posterior angles extended and abruptly rounded. Cheeks triangular and produced 

 behind. 



"Glabella subpentagonal; transverse, usually having the width \ l /2 times as great 

 as the length; tumid, produced, and covered with pustulose tubercles. The upper 

 and middle furrows are faint, but the basal furrow is strong and deep. The basal lobe 

 of the glabella strongly outlined by the basal furrow above, the occipital furrow below, 

 and by the rapidly converging axial furrows. It is short, with a detacbjed node at each 

 extremity. 



"The occipital ring is strongly elevated, usually rising to a pointed node in the 

 center and with two less distinct nodes at the sides. 



•The description to this point is given by Hall on the explanatory page for plate LXXIII 

 and is the correction for this part of his description on page 355. 



