94 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I44 



slight groove extending from margin of periproctal opening to lower 

 edge of test; peristome central to slightly anterior, higher than wide, 

 pentagonal ; floscelle well developed with strong bourrelets and broad, 

 single-pored phyllodes with two series of pores in each half ambula- 

 crum with 8 to 10 pores in the outer series, 2 to 4 in the inner; 

 buccal pores present. 



Comparison with other genera. — Oolopygus is very similar to 

 Catopygus in general appearance, both having a small, elongate test 

 with narrow, equal petals with pores of a pore pair either equal or 

 the outer pore elongated transversely. The periproct is longitudinal 

 and similarly located on the margin, and in both genera the peristome 

 is higher than wide and pentagonal. They differ in that Catopygus 

 has double pores in the phyllodes and no buccal pores, whereas 

 Oolopygus has single-pored phyllodes and buccal pores. Oolopygus 

 occurs later in the Cretaceous than most of the species of Catopygus 

 and is clearly a descendant of Catopygus as shown by its more ad- 

 vanced phyllodes. 



Remarks. — There has been considerable confusion over the nomen- 

 clature of the type species of this genus. There are two species from 

 the Maestrichtian of Belgium which are very similar, and one of 

 these is the type species. Leske (1778) described, but very poorly 

 figured, Echinites pyriformis. Goldfuss (1826, p. 141) referred 

 some specimens to Leske's E. pyriformis, but some authors have not 

 considered his specimens conspecific with Leske's. d'Orbigny (1856, 

 pis. 976-977) in the plates for "Paleontologie francaise, terrain 

 Cretace," figured and named two new species in his new genus 

 Oolopygus, O. bargesi and O. pyriformis. d'Orbigny, in the same 

 work, had placed Echinites pyriformis Leske in Catopygus. Cotteau 

 (i860, p. 457), in the text for "Paleontologie francaise, terrain 

 Cretace," incorrectly credits Goldfuss with the authorship of 0. pyri- 

 formis and designates it as the type species of Oolopygus. Later 

 (1869, P^^- franc, Jur., p. 124) he stated that Oolopygus bargesii was 

 the type species. Lambert (1909, p. 20) erected a new species, 

 Oolopygus gracilis, for O. pyriformis d'Orbigny, non Echinites 

 pyriformis Leske. Echinites pyriformis is also an Oolopygus and is 

 a senior homonym of d'Orbigny's O. pyriformis. 



Mortensen (1948, p. 160) considered Oolopygus as a subgenus of 

 Catopygus. The presence of single pores in the phyllodes and the 

 presence of buccal pores distinguishes this genus from Catopygus. 

 Mortensen evidently was not aware of this difference in the phyllodes. 



I have included photographs of Lambert's figured specimen of 



