NO. 3 CASSIDULOID ECHINOIDS — KIER 169 



proct instead of transverse, a test highly inflated at its posterior 

 margin, and no inner pores in its phyllodes. 



Hypsopygaster resembles Nucleopygiis in its small test, inconspicu- 

 ous petals, and slightly developed phyllodes, but differs in having 

 a marginal periproct, a monobasal apical system with only three 

 genital pores, and strongly developed bourrelets. 



Mortensen (1948, pp. 233, 236) considered Hypsopygaster as a 

 synonym of Studeria mainly because H. ungosensis also has only 

 three genital pores. However, the type species of Studeria, S. elegans, 

 is a larger form, has no inflated posterior, has much more developed 

 petals, and lacks pointed bourrelets. 



Range and distribution. — Danian of Russia. 



DESCRIPTION OF TYPE SPECIES 



HYPSOPYGASTER UNGOSENSIS Bajarunas 

 Plate 25, figures 8-10; plate 26, figures i, 2; text figures 143, 147 

 Hypsopygaster ungosoisis Bajarunas, op. cit., p. 230 (not seen). 



Material. — Twelve specimens studied from the Geological Museum 

 of the Academy of Sciences at Leningrad ; some of them are para- 

 types. 



Shape. — Small, average length 12 mm., elongate, posterior margin 

 truncated producing an oblique face sloping outward causing a dorsal 

 overhang ; greatest width at center, greatest height near posterior 

 margin at top of posterior truncation. 



Apical system. — Anterior (text fig. 147), monobasal, three genital 

 pores, left anterior pore absent, ocular plates very small. 



Ambulacra. — Petals subpetaloid, not visible on unweathered speci- 

 men, pores of pore pair equal, not conjugate ; petals short, equal in 

 length, extending one-half distance to margin (text fig. 147), open, 

 interporiferous zone less than twice width of poriferous zone; five 

 to seven pore pairs in each poriferous zone ; ambulacral plates single 

 pored beyond petals. 



Periproct. — High on posterior truncation, slightly visible from 

 above on some specimens, longitudinal, slight groove below opening. 



Peristome. — Anterior, higher than wide, sunken. 



Ploscelle. — Bourrelets strongly developed, pointed, extending out 

 over peristome opening; phyllodes (text fig. 143) sunken, broad, 

 single pored, arranged in one series in each half-ambulacrum, three 

 or four pores in each ; buccal pores separated from peristome by rim 

 joining bourrelets ; sphaeridia in a double series along midline. 



