October, 1913. New Trilobites — Slocom 49 



fork from the other side in a continuous curve or slight angulation, 

 never in a distinct angle; the other fork passes over the margin and 

 curves across the doublure to the base of the hypostoma. (PI. XIII, 

 fig. 2.) Hypostoma forked posteriorly, only slightly constricted at the 

 base, greatest width about three-fifths the length. Compared with 

 /. gigas the forks point more directly backward making the notch 

 between them narrower. Eyes lunate, prominent, situated less than 

 their own length in front of the posterior margin of the cephalon, rather 

 near together for the genus. A rather indistinct posterior cheek fur- 

 row extends across the fixed cheeks. Occipital ring and furrow obsolete. 



Thorax composed of eight segments. Dorsal furrows shallow, ill- 

 defined; axial lobes depressed convex, not tapering, occupying more 

 than one-third but less than one-half the width of the thorax; pleural 

 lobes curving gently upward from the dorsal furrows, then more abruptly 

 downward to the lateral margins; each segment arching gently forward 

 on the axial lobe, and curving slightly backward towards the extremities 

 of the pleurae. A shallow concave furrow crosses the axial lobe, originat- 

 ing on the posterior margins at the dorsal furrows. A more pronounced 

 subangular furrow originates on the anterior margin of each pleura at 

 the dorsal furrows and passes diagonally outward and backward about 

 three-quarters the length of the pleura. The distal portion of each 

 pleura is distinctly flattened anteriorly. The flattening occupies nearly 

 the entire width at the rounded extremity of the pleura but gradually 

 narrows towards the dorsal furrow until it disappears. 



Pygidium slightly narrower and longer than the cephalon, rather 

 more convex, with a marginal border of uniform width. Axial lobe 

 tapers abruptly near its anterior margin thereafter only moderately to 

 its prominent, rounded termination, no annulations visible. The seg- 

 mentation of the pleural lobes is obscure although three or four segments 

 may be distinguished on young individuals. All markings are more 

 distinct on young than on older individuals. 



Measurements. The figured specimen (Mus. No. P 11 241) (PI. 

 XIII, fig. 1) measures: Cephalon 36.5 mm. long, 63.5 mm. wide, 

 thorax 33 mm. long. Another (Mus. No. P 6969) measures: Cephalon 

 21 mm. long, 36 mm. wide, thorax 18.5 mm. long, 36 mm. wide. Pygi- 

 dium 24.4 mm. long, 34 mm. wide, entire length 63.9 mm. 



Remarks. — Specimens of this species have been usually referred 

 to /. maximus Locke, but the writer is convinced that they belong to 

 Owen's species as the Museum collection contains one nearly complete 

 individual and quantities of less complete ones that were collected at 

 the type locality which agree with Owen's description. The character 

 which most easily distinguishes /. iowensis from /. maximus is the 



