CLARK.] COPTOSOMA MORTONI. 51 



by tell incisions into well-defined lobes, those of the aiubnlacra broader 

 and extending- farther into the opening than the others (PI. xvi, Fig. tib). 



Tlie distal opening is pentagonal, the angles occurring at tlie point of 

 the medial suture of the interanibulacra (PI. xvi, Fig. -}<(). 



Related forms. — Diplopodia HiUi appears at first glance (;losely allied 

 to, if not identical with, PseHdodiadema texauion. It is separated from 

 the same, however, by its larger size, subpentagonal form, and increase 

 in number of pores from the ambitus to the apical disk. In this latter 

 particular it is not unlike Z>. te.vanum, from which, however, it is sepa- 

 rated by its smaller size, subpentagonal form, and two instead of four 

 rows of primary tubercles. It is similar to i*. Khodani of the European 

 Cretaceous in some particulars, but that form is without the increase in 

 number of pores on the upper surface and likewise possesses more plates 

 in each column. 



Locality and geological horizon. — This species is from the ^Vustin chalk 

 (upper Cretaceous) of Texas. 



Collections.— U. S. National Museum; Prof. Kobt. T. Hill. 



COPTOSOMA Desor. 



COPTOSOMA MoKTONi (de Loriol). 



Plate XVII, Figs. la-e. 



Cijplwsoma Mortoni de Loriol, 1887. Recueil Zoologique Suisse, Tome iv, No. 3, 

 pp. 389-391, PI. XVII, Fig. 2a-c. 



Determinative characters. — Test circular, depressed. Ambulacra very 

 wide, with two rows of primary tubercles, thirteen in each row, the 

 three or four at the ambitus large and nearly continent, but diminish- 

 ing rapidly in size toward either pole; poriferous zones narrow, sinu<5us; 

 pores unigeminal, those of each pair separated by a granule. Inter- 

 ambulacra with two rows of tubercles, nine or ten in each row. Mouth 

 opening very large. 



Dimensions. — Transverse diameter, .i to | inch; height, ^ inch. 



Description. — The writer has been unable to obtain a specimen of 

 this species, but the very full descrii)tion and excellent figures given 

 by de Loriol admit of its satisfactory identification. The description 

 that follows is a translation in nearly every particular of that given by 

 de Loriol. The two specimens in the possession of de Loriol were so 

 deformed that he could not determine the height accuratel}'. The 

 test is circular and depressed. The ambulacra! areas are relatively 

 very wide, almost as large as the interambulacral, and bear two rows 

 of large tubercles, thirteen in each row. The first four or five tubercles 

 from the apical disk are far apart and very small. At the ambitus 

 three or four of the tubercles are very large, with nearly confluent 

 areolas (PI. xvii. Fig. Ic), but rapidly diminish in size toward t'le 

 lower surface, the last four or five being very sinall and with diffi- 

 culty distinguished. The areolas, except at tlili ambitus, are n(jt large. 



