222 ECHINODERMATA—ECHINOIDEA SUB-BRANCH III 
small, numerous ; spines minute, acicular. Periproct circular; basal plates 

Fic. 354. 
Melonites multipora, Norwood and Owen. Sub-Carboniferous ; St. Louis, Missouri. A, Test, 1/2 natural size. 
3B, Dorso-central system, slightly enlarged (after Meek and Worthen). 
with three to five genital perforations ; radials sometimes with a single pore. 
Sub-Carboniferous ; North America and Europe. 
[As shown by Jackson and Jaggar (Studies of Melonitidae), the IAmb of Melonites 
enter the peristomial margin as two plates. Passing dorsally, new columns are introduced, 
rapidly at first, until the full complement is reached at or a little above the ambitus. The initial 
plates of new columns are pentagonal, with a more prominent apex of the pentagon pointing 
ventrally ; and an adjacent plate is characteristically heptagonal, thus facilitating the orienta- 
tion of obscure fragments. Newly added plates near the dorsal area are more or less rhombic 
in outline. The Amb terminate actinally in four plates ; and new vertical columns are added 
between the median and lateral columns on either side, increasing dorsally. ] 
Lepidesthes, Meek and Worth. Test large. dmb broad, with eight to 
eighteen columns of small plates imbricating adorally ; and pores in single, 
or occasionally in double pairs. 4m) with three or more columns of plates 
imbricating aborally and laterally. Sub-Carboniferous ; North America. 
Hyboechinus, Worthen and Miller ; Pholidocidaris, Meek and Worthen. 
Sub-Carboniferous ; North America. 
Family 3. Tiarechinidae. Zittel. 
Ambulacra narrow, with two vertical rows of plates pierced by a pair of pores. 
Interambulacra with a single peristomial plate, 
followed by three vertically elongated plates only, 
one on either side of the narrower median plate. 
Basals large, with two genital perforations ; 
radials smaller, imperforate, and notching the 
union of the basals slightly. 

Tiarechinus, Neumayr (Fig. 355). The test 
of this unique genus is very small, flat actinally, 
Fra. 355. 
Tiarechinus princeps, Laube. UpperTrias; and sub-hemispherical dorsally. Below the 
St. Cassian, Tyrol. Ventral and lateral ambitus and actinally the ornament consists 
aspects, highly magnified (after Lovén). s ! 
of a plain primary tubercle to each plate ; else- 
where the test is coarsely granular, including the very large apical system. The 
solitary species, 7’. princeps, Laube sp., occurs in the Trias of St. Cassian, Tyrol. 
