8 PROP. p. M. DUNCATS'S EEVISION OF THE 



Genus Botheiocidaeis, Eichwald, 1860, Lethcea Bossica, p. 654. 

 Fr. Schmidt, 1874, Mem. Acad. St. Fetersh. ser. 7, vol. xxi. 

 no. xi. pp. 36-38. Zittel, 1876-80, Falcsont. Bd. i. p. 481. 

 Loven, 1883, Pourtalesia, p. 57. {Slightly altered.) 



Test small, hemispherical or conico-hemisplierieal. 



Apical system central dorsal, with five large broad radial plates 

 limiting the periproct, each with two pores surroimded by a raised 

 rim, with five small, imperforate, triangular basal plates inter- 

 vening between the radial plates, entering or not the periproct. 

 Six or eight ovoid, acuminate anal plates, each with a spiniferous 

 tubercle. 



Ambulacra wider than the interradia, straight, with two rows 

 of plates, large, hexagonal at the ambitus, and smaller above and 

 below; each plate with a central circular pit, with a pair of 

 pores on its floor, and with 2-4 small, perforate, wart-like 

 tubercles, carrying finely longitudinally-striated small spines ; 

 around is some granulation. The ambulacra end dorsally at the 

 large radial plates and actiually at the peristomial margin, where 

 they are moderately broad and exclude, by their contact, the 

 interradial plates. 



Tentacles long and cylindrical. {Loven.) 



Interradia five in number, narrow, composed each of one row 

 of plates Bubequal to the ambulacral, but smaller dorsally and 

 actinally, excluded from the peristomial margin. Plates may 

 have small tubercles and granules. 



Peristome subcircular, margin formed by the ambulacra ; five 

 narrow triangular buccal plates project inwards. 



Fossil. Lower Silurian : Europe. 



Order II. PEEISCHOECHINOIDA, McCoy, 1849, 

 Ann. Sf Mag. Nat. Hist. vol. iii. (Amended.) 

 Tests regular, with more than two vertical rows of interradial 

 plates which are dissimilar ; with two or many vertical rows of 

 ambulacral plates, each with a pair of pores. Test thick and 

 rigid, or thinner and with the plates overlapping more or less. 

 Ornamentation variable. Jaws present. 



Earaily Aech^ocidaeidje. 

 Perischoechinoida with narrow ambulacra, each with only two 

 rows of poriferous plates. 



