298 



ECHINODERMATA— ECHINOZOA 



PHYLUM IV 



rostrum token such is present. Ambulacra flush. 



apetalous, sometimes discontinuous ; 

 pores single or slit-like. 



Pourtalesia, Spatagocystis 

 and Echinocrepis A. Agassi z. 

 Recent. 



Order 5. PLESIOCIDA- 

 ROIDA Duncan. 



Test regular, endocyclic. 

 Genitals largely covering the 

 dorsal surface. Two columns of 

 loiv simple plates in each avi- 

 hulacral area and three columns 

 of plates in each interambulacral 

 area. Plates not imbricate. 

 Primordial interambulacral 

 plates in hasicoronal row. Base 

 of corona not resorbed. Oculars 

 small, strongly exsert by the con- 

 tact of large genitals. Peri- 

 proct central, structure unknown. 

 Peristome central, structure un- 

 known. Lantern and perigna- 

 thic girdle unknown. 



Family 1. Tiarechinidae 



ZWiA. 



The single primordial plate 

 of the interamhulacra followed 

 hy three elongated plates only, 

 one on either side of a narrow 

 median plate. Trias. 



Tiarechinus Neumayr (Fig. 426). The test of this unique genus is very 

 small, flat actinally, and sub-hemispherical dorsally. Below the ambitus and 

 actinally the ornament consists of a plain 

 primary tubercle to each plate ; elsewhere the 

 test is coarsely granular, including the very 

 large apical system. The solitary species, 

 T. princeps (Laube), occurs in the Trias of St. 

 Cassian, Tyrol. 



Our knowledge of this genus and family is 

 based largely on Lov6n's study of a single 

 minute specimen. As it has three columns 

 of plates in an interambulacral area, it is 

 considered a further remove from the primi- 

 tive than those types with two columns. Three plates, representing three 

 columns, immediately succeeding the primordial interambulacral plate, is a 

 unique character in Echini. 



Fig. 4-Jo. 



Macropneustes inencghinii Desor. Eocene ; Monte Spiado, near 

 Vicenza. 



Fig. 426. 



Tiarechinus p-?r!cc/)>- (Laube). Upper Trias ; 

 St. Cassian, Tyrol. Venti-al and lateral 

 aspects, much enlarged (after Loven). 



