ISOTELUS. 35 



them as do those of that species. The direction of the endopodites is diagonally forward, 

 and the outer portions do not appear to be curved backward as in Isotelus maximus. It 

 would appear also that the endopodites were nearly or quite long enough to reach the outer 

 margin of the dorsal test. On no endopoclite can more than three segments be definitely dis- 

 tinguished, but the longest ones are the most obscurely segmented. 



No appendages are preserved on the pygidium, but at one side of the median groove 

 there are two projections which may be processes to which the appendages were attached. 



Measurements: Total length of specimen, 109 mm. Probable length when complete, 

 116 mm. Length of cephalon, 40 mm.; width at genal angles, restored, about 62 mm. 

 (Billings' restoration). Width of doublure of front of cephalon on median line, 17 mm.; 

 length of hypostoma, 20 mm. Length of coxopodite of last appendage on left side of 

 cephalon, 10.5 mm.; length of basipodite of the same appendage, 5 mm. Diameter of cox 

 opodite, 2 mm.; diameter of basipodite, 1.5 mm. Length of coxopodite on left side oi 

 the second segment of the thorax, u mm.; diameter, about 2.5 mm. Length of basipodite 

 of the same, 5 mm.; diameter, about 1.5 mm. Length of ischiopodite, 3.5 mm.; diameter, 

 about 1.5 mm. Length of meropodite, 2.5 mm. (this may be less than the total length as 

 the segment is not completely exposed.) Distance between proximal ends of gnathobase." 

 of the fifth thoracic segment, about 7 mm. Distance between outer ends of the coxopo- 

 dites of the first thoracic segment (estimated from measurements on the left side), 27 mm 

 Distance apart of the dorsal furrows at the first thoracic segment, 27 mm. Length of the 

 longest exopodite which can be traced, about 20 mm. 



Isotelus maximus Locke. 

 (PI. 10, fig. 2.) 



Illustrated: Mickleborough, Jour. Cincinnati Soc. Nat. Hist., vol. 6, 1883, p. 200, figs. 1-3 (endopodites 

 and coxopodites). Walcott, Science, vol. 3, 1884, p. 279, fig. I (endopodites, coxopodites, and traces of 

 exopodites). Woodward, Geol. Mag., dec. 3, vol. I, 1884, p. 162, figs. 1-3 (copies of Mickleborough's 

 figures). Bernard, The Apodidx, 1892, text fig. 49. Beecher, Amer. Jour. Sci., vol. 13, 1902, p. 169, pi. 5. 

 figs. 5, 6 (outline from one of Mickleborough's figures and an original figure). Walcott, Smithson. Misc. 

 Coll., vol. 67, 1918, p. 133, pi. 24, figs. 3, 3a ; pi. 25, fig. I. 



This specimen, which conies from the Richmond strata 2 miles north of Oxford, Ohio, 

 is the best preserved of the specimens of Isotelus with appendages which has so far been 

 found. The individual consists of two parts, the actual specimen, and the impression of 

 the ventral side. 



To describe it I am using very skillfully made plaster reproductions of both parts, 

 presented to the Museum of Comparative Zoology by Doctor Charles D. Walcott, and pre- 

 sumably made after he cleaned the specimen as described in Science (1884). I have also 

 an enlarged photograph (pi. 10, fig. 2) which seems to have been made after some later 

 period of cleaning, probably by Professor Beecher, and I have examined the original speci- 

 mens in Washington. 



Viewed from the dorsal side, it is seen that the individual is very imperfect, the greater 

 part of the cephalon being removed by a diagonal bre.ak which cuts off the anterior third 

 of the left eye and extends to the front of the second thoracic segment on the right side. 

 The ends of the pleura of both sides of the thorax are broken away, as are also the greater 

 parts of the pleural lobes and the posterior end of the pygidium. On the ventral side, merely 

 the posterior tips of the hypostoma remain, but the distal ends of the appendages were so 

 far within the outer margin that the appendagiferous area is quite fully retained. 



