52 MESOZOIC ECHINODERMATA OF THE UNITED STATES. [bull. 97. 



The bosses are finely cremilated and the manielons small aud imper- 

 forate. Upon the lower surface there are large mammillated grannies 

 which can be with difficulty distinguished from the i)rimary tubercles. 

 Each areola is also partially surrounded by a circle of small granules 

 that occur most numerously near the line of the central suture. The 

 granules are few in number on the upper surface. The poriferous zones 

 are narrow, slightly sinuous, and corax)Osed of small pores without any 

 increase toward the apical disk or mouth opening. A small granule is 

 found between the jjores of each pair (PI. xvii, Fig. Ic). 



The interambulacral areas bear two rows of primary tubercles that 

 are similar to those of the ambulacra, but larger and less numerous 

 (PI. XVII, Fig. la). The lower surface is covered by large mammillated 

 granules that can scarcely be distinguished from the tubercles, and 

 also by numerous small ones. There are few granules on the ui^i^er 

 surface. The mouth opening is large, with slight incisions. 



Related forms. — This species is most closely related to Coptosoma 

 speciosum, but in form and in several details of strncture is unlike it. 

 The presence of granules between the pores of the present species is a 

 marked feature. 



Locality and geological horizon. — This form is from the Rotten limestone 

 (upper Cretaceous) of Nahalak, Kemper county, Mississippi. 



Collection. — P. de Loriol, Switzerland. 



Coptosoma speciosum Clark. 

 Plate XVIII, Figs. la,-h. 



CypTiosoma speciosum Clark, 1891. Johns Hopkins University Circulars, No. 87, p. 76. 



Determinative characters. — Test circular, inflated at the sides, flat- 

 tened on the upper and lower surfaces. Ambulacra wide, with two 

 rows of primary tubercles, twelve or thirteen in each, that gradually 

 diminish in size toward the poles; poriferous zones sinuous; jjores uni- 

 geminal. Interambulacra with two rows of tubercles slightly larger 

 than those of the ambulacra. IVIouth opening one-third the diameter 

 of the test. 



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



Description. — This delicate species has a circular test with inflated 

 sides. Both poles are flattened, the lower more than the upper (PL 

 XVIII, Fig. 16). 



The ambulacral areas are wnde and prominent, and bear two rows of 

 large tubercles, twelve or thirteen in each row. The areolas are nearly 

 confluent above and below, and are striated by irregular radiating ridges 

 (PI. XVIII, Fig. 1/). The bosses are deei)ly crenulated, and the small 

 manielons are imperforate. Minute tubercles and granules irregularly 

 surround the ])rimary tubercles, occurring in greatest number along 

 the central suture. The poriferous zones are slightly sinuous, the 

 three pore pairs having a. curved arrangement on each ambulacral plate. 



