NATURAL SCIENCES OF PHILADELPHIA. 53 



Glabella rather depressed convex, wide anteriorly and narrowing posteriorly 

 n. t \ , fuiT0 , w '- JU f in froflt of vrhich, and connected with the palpebral 

 lobes on each side it has a single small, obscure lateral lobe; neck furrow 

 broad and well denned both across the glabella and across the posterior mar- 

 gmsof the cheeks; neck segment rather wide, depressed below the level of 

 the highest part of the glabella in front of it. Eyes of moderate size, reniform 

 nearly as prominent as the glabella, placed but little in front of the continual 

 tion of the neck furrow across the cheeks, apparently smooth, but showing 



when tne outer crust is removed, numerous very minute lenses be ith! 



Cheek sloping off rather abruptly from the eyes to the thickened margin 

 which does not continue around the front of the glabella; facial sutures ra- 

 ting the anterior margin in front of the eyes before, and a little outside of 

 them behind. 



Thorax nearly twice as wide as long, distinctly trilobate; mesial lobe but 

 moderately prominent, nearly twice as wide as either of the lateral lobes its 

 eight segments merely rounded and without furrows. Lateral lobes narrow 

 pleura? curving moderately downwards at less than half their length out from 

 the axial lobe, but not distinctly geniculated, each provided with a furrow ex- 

 tending nearly half-way out. Pygidium approaching semi-circular, with the 

 anterior lateral angles obliquely truncated ; mesial lobe but slightly wider an- 

 teriorly than the lateral ; segments about eleven ; lateral lobes with ei'ht or 

 nine segments. 



Surface finely granular, the granules being most distinct on the glabella, 

 and the segments of the mesial lobe of the thorax. 



This species will be at once distinguished from our P. PorllocJcii, from the 

 same horizon, by its much broader and less ventricose glabella, and the pecu- 

 liar tuberculiform eyes of that species, as well as by the broader and less pro- 

 minent mesial lobe of the pygidium, in the form under consideration. 



Locality and position. Crawfordsville, Indiana. Keokuk division of the 

 lower Carboniferous series. 



Asaphus (Isotelds) vigilans, M. and W. 



Body small, elliptic in general form, and moderately convex. Head rather 

 more than half as long as wide, approaching a subcrescentic outline, with the 

 posterior lateral angles abruptly rounded or subangular; anterior margin ap- 

 parently somewhat narrowly rounded ; posterior outline broadly and distinctly 

 concave, but rather straight along the middle, without any traces of marginal 

 or occipital furrows. Glabella not rising above the general convexity of the 

 head, and entirely undefined by any traces of dorsal furrows. Eyes situated 

 about their own antero-posterior diameter in advance of the posterior margin, 

 and apparently about half way between the latter and the front, rather Widely 

 separated from each other, and very prominent, nearly round, and truncato- 

 sub-conic in form ; visual surface elevated almost entirely above the general 

 convexity, and curved around so as to form about three-fourths of a circle, 

 presenting a smooth surface ; palpebral lobes as elevated as the eyes, and much 

 contracted, or merely connected with the glabella on the inner side by a 

 narrow neck. Facial sutures extending obliquely outward and backward from 

 the eyes behind, so as to intersect the posterior margin about half-way be- 

 tween a line drawn longitudinally through the middle of each eye, and the 

 posterior lateral margins of the cheeks; and in front, at first curving slightly 

 outward a little in advance of each eye, beyond which point they converge 

 forward so as apparently to intersect the front margin in such a manner as to 

 leave a rather narrow anterior edge to the glabella.* 



Thorax longer than the head or pygidium, as measured over the curve of a 



* As the specimen is imperfect here, it is possible these sutures may not reach the an- 

 terior margin in front. 



1870.] 



