76 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I44 



greatest width and height often posterior to center ; apical system 

 anterior, tetrabasal, four genital pores ; petals of approximately equal 

 length, flush, open, or with slight tendency to close, with outer pore 

 of pore pair more elongate than inner, all ambulacral plates double 

 pored; periproct supramarginal or almost marginal, always at least 

 slightly visible from above ; often with groove extending from lower 

 edge of periproct opening to adoral edge of test ; peristome anterior, 

 pentagonal, slightly higher than wide ; bourrelets fairly well devel- 

 oped; phyllodes slightly broadened, with two series of double pores 

 in each half -ambulacrum, approximately eight in each outer series, 

 five in each inner; pore of each pair often reduced in size; no 

 buccal pores. 



Comparison with other genera. — Phyllobrissus is very similar to 

 Catopygus, and it is difficult to decide whether or not this genus 

 should be maintained. Lambert (1902, p. 15) and Mortensen (1948, 

 p. 167) suggested that Phyllobrissus might be considered as a sub- 

 genus of Catopygus. Their type species are very similar in general 

 appearance. Both have the same petal arrangement, strikingly similar 

 phyllodes, with two series of pore pairs in each half-ambulacrum, 

 and with the inner pore of each pair greatly reduced in size. They 

 differ in that P. gresslyi is slightly broader, with a more depressed 

 adapical surface, and an obliquely truncated posterior margin expos- 

 ing the periproct adapically. In C. carinatus the posterior margin is 

 pointed, and the periproct is not visible from above. Although these 

 differences may be sufficient to distinguish generically these two 

 species, there are some species which have some of the characters 

 of both these species, and it is difficult to decide to which of the two 

 genera to assign them. 



Phyllobrissus is also very similar to NucleoUtes, with both genera 

 having narrow, straight, open petals, and very similar phyllodes. 

 Phyllobrissus differs in having a more elongate test, more developed 

 bourrelets, and a more marginal periproct. 



Remarks. — Cooke (1953, p. 17, and 1955. p. 97) refers to Phyllo- 

 brissus two American species, Petalobrissus cubensis (Weisbord) 

 and Nucleopygus angustatus (Clark). I do not agree with this 

 assignment. Petalobrissus cubensis has a much more developed 

 floscelle with single-pored phyllodes (text fig. 106) and buccal pores, 

 as opposed to the double-pored phyllodes and lack of buccal pores 

 in Phyllobrissus. Furthermore, the apical system in Petalobrissus 

 cubensis is monobasal, whereas it is tetrabasal in Phyllobrissus. 



