pice between the lde of th . the h.-ad of tl- picur.i dth of the space Is between 



third and : he width of n . Th.- pl.-i, ,t ut the fulcra at an ancl-- which varies ID 



different inili- and .it ie lU th.-ir length from the side of the I 



.rtcr than th- >>: from moderate]* I.. 



. and uniformly rounde<l: the anterior nearly half the 



leiik'lh of the iivcidiiim: the -.lraii;hl -hi.- lornied hy the truncation forming an angle of from 40* to 

 60* with the longitudinal aiK of the 1,. : : > .::dlum I- well defined at the ai. 1 



margin l>> wluchd ul at at-Mit one-third orone halMhe]ei,k'th, onverglng towards 



each other, and sometime* . ..-I'.niin: the .1; 



-oftheci- ir although - .able. The specimen on 



which th- '-Minded, h.i- th.- R .e head and pytfidmni covered with short 



!M|iiannis- .f each fissure lietm.' more elevated than the other, gives to the HUT- 



: from half a line to two or three linen, all' 



from one-eighth to one f.Mirth of a line di-tant from each other, t >n the tail they seem to radiate lrr.- k 'u- 

 axIsMaccMt- the front margin and parallel with It, arc a number of straight 



iilou- tl-sures. Tl. r specie* Of tin III other -iM-cimens the 



;iar.-..f the name character. Ir n-n In Dr. Grant'* 



he middle portion of the front of the head is nearly uniooth, and In addition to the strlas Is 

 coarsely puncture<|. 



Mr. Hillings also called attention to the close approach of /. //<.//<.///> to 7. 



Ir-iwln Wahlenher^': and 1 am of the opinion that the same fossil had been 



' il>ed l.y Hall in 1S47 (loc. cil.) under the latter name. 



It appears from the ol n- made by Holm* that this species (/. <-nixsiftn<lti 



Wahl.) ha- been generally mi-apprehended from the date of its description (ls_l). 

 Holm has redescribed the specific characters from the type specimens, and, as a 

 result, eliminates from this association all other fossils which have been compre- 

 hended under this designation. Thus restricted, the author regards Ihe species as 

 unknown outside of Dalecarlia, Sweden, and as having a very short vertical range 

 from the youngest layers of the Orthoceras-limestone to the oldest of the Cystidean- 

 limestone" (an immediately succeeding zone). With /. crassicauda thus limited. /. 

 urn- rii-'inin appears to be its nearest relative; indeed, there is excellent reason for 

 holding the latter but a variety of the former. The similarities in the two are both 

 general and detailed; the differences which may lie indicated are a somewhat deeper 

 anterior convexity of the ceplialon in the American form, a less sharply limited 

 glabella and py^idial axi<. otherwise the contour of the parts, all and several, the 

 surface sculpture witli it- variation- on the dillerent parts, marginal outlines and 

 curve- of facial -ut tires are all alii 



Some of the internal casts of the ceplialon from the lialena limestone at Wykoll 

 show, at the anterior termination of the dorsal furrows, two lunate cicatrices 

 like those mentioned in the de-cription of />'w/-7i/x tri'titnm-naix and />'. orbicfmifatiit, 

 In finely preserved specimens from the Trenton of New York there is seen to be a 

 smooth interruption of the external ornamentation directly over these spots. The 

 Minnesota specimens are usually in a dismembered state and are frequently some- 



Zelurbr. drr datch. rook*. OmclUcb.. vol. \\\\\. p. iOt. pi a. 1MO. 



