BOTHRIOCII)ARIS. 



of test not imbricate. Primordial interambulacral plates are in the basicoronal row. Baai- 

 coronal ambulacral plates are not sharply distinguished from the perwtomal plates. Spines 

 few on ambulacral and interambulacral, or on ambulacral plates only. IVri-tom.- will, 

 rows of ambulacral plates only. Oculars very large, genitals small. IVripnx-t with man y small, 

 angular plates, filling the area. Ordovician, Russia. This is the oldest known K.TIUS of Echini 

 and also one of exceptional interest on account of its features which in many respect* resemble 

 the young of later Echini. The type species is Bothriocidaris globulus Eichwald, from the Ordo- 

 vician of Russia. (See pp. 54, 64, 70, 80, 87, 149, 208.) 



Key to the Species of Bothriocidaru. 



Oculars continuous, forming a closed ring; small genitals dorsal to the oculars; tubercles on ambulacral 

 and interambulacral plates, . ... . H. arrhaicn sp. nov.. p. 239. 



Oculars in part continuous and in part separated by the small genitals; tubercles on ambulacra! plates 

 onl y. B. paA/rm Schmidt, p. iM_ ( 



Oculars all separated by the small genitals; tubercles on ambulacral and interambulacral plates, 



B. globulin Eichwald, p. 243. 



'Bothriocidaris archaica sp. nov. 

 Text-figs. 2, p. 54; 22, p. 70; 40, p. 80; 162, p. 149; Plate 1, figs. 1, 2. 



Bothriocidaris globulus (pars) Jaekel, 1894, text-figs. 1, 2: (pars) A. Agassiz, 1904, p. 79; (pars) Klem. 



1904, p. 15. 

 Bothriocidaris [globulus pars] Bather, 1902, p. 620, text-fig. 5B. 



The precious and only known specimen of this species is in the Museum fur Naturkunde 

 in Berlin, and I am under greatest obligations to Dr. Otto Jaekel for the opportunity to study 

 this which, I feel, is perhaps the most interesting of known Echini. The details of structure 

 are remarkably clearly preserved, but are naturally difficult to study in such a small specimen. 

 It is probably the best preserved specimen known in the genus, and is marvellously perfect 

 when its age is considered. Its perfection is a tribute to Dr. Jacket's skill as a preparator. 



The test is slightly elliptical, 12 mm. in height, 11.2 mm. in diameter through the mid- 

 zone. The circumference at the ambitus is 35.5 mm.; circumference in a vertical plane around 

 the poles 36 mm., width of an ambulacrum at the mid-zone 4.2 mm., width of an interambula- 

 crum at the same area 2.2 mm. Each ambulacrum consists of two columns of high hexagonal 

 plates; at the mid-zone a plate measures 2.2 mm. in its greatest width. Ambulacral pores are 

 superposed in a sunken area in the center of each plate. At the ambitus there are typically 

 four, in some cases perhaps fewer, tubercles on each plate near the margin of the peripodium. 

 Interambulacral plates are high, hexagonal, equaling the height of the ambulacrals. with from 

 one to three tubercles on each plate at the mid-zone. The plates of the corona are not im- 

 bricate. There are two rows of peristomal ambulacral plates. The diameter of the apical 



