^6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I44 



cral plates beyond petals double pored except in Oolopygus, phyllodes 

 narrow to slightly widened, with two series of pores in each half- 

 ambulacrum, no buccal pores except in Oolopygus; bourrelets moder- 

 ately developed; adoral tubercles the same size or slightly larger 

 than adapical, no naked granular zone in interambulacrum 5. 



Genera. — Niicleolites, Pseudosorella, Clypeopygus, Catopygus, 

 Phyllobrissus, Pygaulus, Pygorhynchus, Pygopistcs, Hypopygurus, 

 Plag'wchasma, Oolopygus, Hemicara. 



Range. — Jurassic (Bajocian) to Cretaceous (Senonian). 



Comparison zvith other families. — The Nucleolitidae are distin- 

 guished from the Galeropygidae by their more developed petals, 

 usually more elongate shape, and usually fewer pores in their phyl- 

 lodes. They are distinguished from the Clypeidae by their narrower 

 petals with narrower poriferous zones, and by the smaller number of 

 pores in their phyllodes. The difference between the two families is 

 not great, for there are some species of Nucleolites that have many of 

 the characters of Clypeus. 



Genus NUCLEOLITES Lamarck 



Nucleolites Lamarck, 180 1. Systeme des animaux sans vertebres, p. 347. Type 

 species by subsequent designation, Lambert, 1898, p. 168, Nucleolites sciitatns 

 Lamarck. 



Synonyms: Acrotfiasus Pomel; Clitopygus Pomel; Clunictdiis Pomel; Echino- 

 brissiis Gray; ? Heteronucleus Lambert; Holcoepygits Pomel; Lophopygiis 

 Pomel; Notopygus Pomel; Taphropygns Pomel; Thigopygus Pomel. 



GENERIC DESCRIPTION 



Small to medium size, usually broad with greatest width posterior 

 to center, moderately inflated with thick margins; apical system 

 tetfabasal, with or without complementary or catenal plates; petals 

 long, open, poriferous zones narrowing distally, pores conjugate, 

 outer pore greatly elongated transversely ; all ambulacral plates double 

 pored; adorally interambulacrum with single plate (text fig. 29) at 

 peristome preceded by regular series of alternating plates ; periproct 

 supramarginal, longitudinal, varying in position from in contact with 

 apical system to widely separated from it, with anal groove extending 

 from apical system or from periproct to posterior margin ; peristome 

 anterior, pentagonal, depressed, usually wider than high; bourrelets 

 moderately developed; phyllodes narrow or slightly widened, double 

 pored, with two series of pore pairs in each half-ambulacrum ; no 

 buccal pores ; tubercles perforate, crenulate, larger adorally than 

 adapically. 



