254 ROBERT TRACY JACKSON ON ECHINI. 



acteristic of the Palaeechinidae. As far as the evidence goes, the primordial ambulacral plates 

 are around the mouth on the peristome, and the primordial interambulacral plates are in the 

 basicoronal row, or are resorbed in the advance of the peristome. The peristome is plated with 

 many rows of ambulacral plates only, or may in addition have non-ambulacral plates situated 

 interradially. Oculars are usually imperforate and all insert, but rarely are perforate, and 

 exceptionally one or more to all may be exsert. Genitals usually have three or more to numer- 

 ous genital pores; the madreporite is rarely distinguishable. The periproct is covered with 

 many angular plates which fill the area. The lantern is inclined, subtending an angle of about 

 90 degrees, and as in modern regular Echini, is composed of forty pieces. The teeth are grooved, 

 pyramids wide-angled, foramen magnum moderately deep, epiphyses narrow, .capping the 

 half-pyramids; brace and compass as in modern Echini. This group includes all Palaeozoic 

 Echini excepting those already considered, and comprises the best known and, excepting Both- 

 riocidaris, the most interesting genera of these ancient formations (pp. 361-363). 



Family Archaeocidakidae M'Coy. 



Echinocrinoidea T. and T. Austin, 1S42, p. 111. 

 Archaeocidaridae M'Coy, 1849, p. 253; Loven, 1874, p. 42. 

 Lcpidocidaridac. Bather, 1907, p. 456. 



The test is spheroidal or depressed; ambulacra are narrow, with in each area two columns 

 of plates imbricating moderately adorally and beveled undei; the adambulacrals. Pore-pairs 

 are uniserial or slightly biserial. There are from four to eight columns of plates in each inter- 

 ambulacral area, plates are large, thin, imbricating moderately aborally and laterally and over 

 the ambulacrals. The interambulacral plates bear a large central perforate primary tubercle 

 and large scrobicule, with a large primary spine, also secondary tubercles and spines. The 

 base of the corona is resorbed in the advance of the peristome, strongly so in Archaeocidaris. The 

 peristome has many rows of ambulacral and at least in Ai-chaeocidaris interradial non-ambula- 

 cral plates as well. Oculars and genitals unknown or very doubtful. There are three genera in 

 the family. The name Lepidocidaridae was proposed by Dr. Bather to take the place of Archae- 

 ocidaridae on the basis of giving up Archaeocidaris for the earlier but misleading name of 

 Echinocrinus. As I have decided to cling to the old established name Archaeocidaris, pending 

 possible consideration of the matter, I therefore retain also the name Archaeocidaridae. 



EociDARis Desor. 



Eocidaris Desor, 1858, p. 155; Lov(5n, 1874, p. 42; Bather, 1909, p. 44; (pars) Lambert and Thiery, 1910, 

 p. 126. 



This genus, most imperfectly known, is based on isolated interambulacral plates and 

 primary spines. Interambulacral plates are probably hexagonal, or pentagonal in adradial 



