I 



164 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I44 



Floscelle. — Bourrelets strongly developed, highly inflated, pointed ; 

 phyllodes single pored (text fig. 136), broad, with five to seven pores 

 in each outer series and one to three in each inner series ; buccal pores 

 present. 



Tuberculation. — Adorally, tubercles much larger, bosses anterior, 

 in deep, anteriorly elongated scrobicules ; naked pitted medial area in 

 interambulacrum 5, ambulacrum III. 



Occurrence. — Maestrichtian of France, Belgium, and Holland. 



Location of type specimen. — Unknown. 



Remarks. — Lambert created Procassidulus as a substitute name 

 for Cassiduhts which he thought was preoccupied. 



Genus NUCLEOPYGUS L. Agassiz 



Nttclcopygus L. Agassiz, 1840a. Catalogus systematicus ectyporum echino- 

 dermatum fossilium musei Neocomensis, pp. 7, 17. Type species by subsequent 

 designation, Lambert, 1898, p. 165, Nucleopygus minor Desor. 



Synonyms : Lychnidius Pomel ; Porobrissus Lambert. 



GENERIC DESCRIPTION 



Small, low, generally oval, well-rounded margin, depressed peri- 

 stome ; apical system tetrabasal, often very eccentric anteriorly ; 

 petals narrow, inconspicuous, usually open, with conjugate pores, 

 ambulacral plates beyond petals single pored ; periproct supramarginal, 

 longitudinal, in groove extending to posterior margin ; peristome 

 pentagonal or subpentagonal, anterior ; bourrelets slightly to mod- 

 erately developed, not pointed; phyllodes single pored, narrow or 

 only slightly widened, very few or no occluded pores ; buccal pores 

 present ; adoral tubercles of same size or only slightly larger than 

 adapical, very narrow naked zone often in interambulacrum 5, often 

 pitted. 



Comparison with other genera. — Nucleopygus is similar to Nucleo- 

 lites in having a supramarginal periproct and short petals, but differs 

 in having less conspicuous, narrower petals, a more elongate test, and 

 single-pored phyllodes with buccal pores. It differs from Petalohrissus 

 in having narrower petals, a smaller test, and narrower phyllodes 

 with fewer occluded pores. It is similar to Rhynchopygus in its petals 

 and shape and size of test, but is distinguished from it by its less 

 developed bourrelets, narrower phyllodes, and smaller adoral tu- 

 bercles. Finally, it differs from Ochetes in having less developed 

 bourrelets, single pored phyllodes, more developed petals, and smaller 

 adoral tubercles. 



