NO. 1117. PROCEEDINGS OF THE NATIONAL MUSEUM. 673 



The thorax has two, smooth, disproportionately large, uucousolidated 

 segnients, both of which at maturity are greatly excavated posteriorly. 

 These two segments are followed by nine smaller abdominal ones, each 

 of which bears medially a parallel series of linear ridges. These 

 ridges are most i)romiuent posteriorly, and terminate on the lateral 

 extensions of the ninth segment. The tenth, or anal segment, is 

 imperfect. It is grooved medially, and probably had two slender 

 lateral cercopoda, as in JD. carri. 



Length of smallest specimen, not including the cercopoda, 11 mm.; 

 greatest width, 8 mm. Lengtli of largest specimen, which lacks the 

 small abdominal segments, 23 mm.; width across the large anterior seg- 

 ments, 19 mm. 



Formation and JocaUty. — In Lower Coal Measure nodules, near Morris, 

 Illinois. Three specimens are known: One, the type, is in the collec- 

 tion of Mr. Iv. D. Lacoe; another was found by Mr. J. C. Carr, and a 

 third, the most perfect example, by Mr. L. E. Daniels. Specimen No. 

 25713, U.S.N.M. 



DIPLODISCUS CARRI, new species. 

 (Plate LVIII, fig. 6.) 



This species is associated with D. diplodiscus. It differs in being con- 

 siderably narrower, and in having but seven small abdominal segments, 

 three less than in the latter form. Moreover, the segments are broader, 

 and posteriorly do not taper so rapidly, as in B. diplodiscus. The anal 

 segment, as far as can be seen, is very wide, deeply grooved, and bears 

 two long, slender cercopoda. These are marked by widely separated 

 transverse lines. 



The specimen exposes the dorsal side, but is crushed in along the 

 center through the two large thoracic segments and the head shield. 

 The drawing shows the detail as observed, but the ventral structure 

 can not be made out beyond the fact that the head bears a series of 

 diverging furrows, probably corresponding to tive pairs of limbs. 



Greatest length not including the cercopoda, 17 mm.; greatest width, 

 9 mm. 



Formation and locality. — A single specimen of this species was found 

 by Mr. J. C. Carr, near Morris, Illinois. The writer takes pleasure in 

 naming the species after its discoverer, in recognition of his intelligent 

 and persistent efforts for many years to unearth the fossil treasures of 

 Mazon Creek. 



PROTOCARIS, Walcott. 



(Plate LVIII, fig. 1.) 



Protocaris, Walcott, Bull. U. S. Geol. Surv., No. 10,1884, p. 50, pi. x, fig. 1; 

 Ibid., No. 30, 1886, p. 147, pi. xv, fig. 1. 



Generic c/mr«e/ers.— Carapace large, smooth, subquadrangular in 

 outline, posteriorly much extended over the abdomen, slightly excavated 

 medially along the anterior margin and more deeply posteriorly; mar- 

 Proc. i^. M. vol. xix 43 



