174 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I44 



Genus CASSIDULUS Lamarck 



Cassidulus Lamarck, 1801. Systeme animaux sans vertebres, p. 348. Type species 



by monotypy, Cassididus cariboearum Lamarck. 

 Synonym : Glossaster Lambert. 



GENERIC DESCRIPTION 



Small, low, elongate ; apical system monobasal, four genital pores ; 

 petals slightly or well developed, straight, open or closing distally, 

 poriferous zones of same petal usually unequal, ambulacral plates 

 beyond petals single pored ; periproct supramarginal, longitudinal or 

 transverse, with groove extending from opening to posterior margin ; 

 peristome anterior, pentagonal, transverse ; bourrelets well developed ; 

 phyllodes widened, single pored with slight crowding of pores, one 

 or two or no occluded pores ; buccal pores present ; adorally, tubercles 

 much larger, scrobicules often polygonal, with bosses eccentric an- 

 teriorly; adorally, naked, often pitted area in interambulacrum 5, 

 ambulacrum III. 



Comparison with other genera. — Cassididus is very similar to 

 Rhynchopygus but differs in having a monobasal apical system as 

 opposed to the tetrabasal system in Rhynchopygus. As Cassididus 

 occurs later, in the Tertiary, whereas Rhynchopygus is from the 

 Upper Cretaceous, and since Cassidulus has a more advanced apical 

 system, there is little doubt that it is descended from Rhynchopygus. 

 Cassididus differs from Rhyncholampas in having a smaller, more 

 elongate test, narrower, nonlanceolate petals, a usually less posterior 

 periproct, and phyllodes with fewer pores. It differs from Hypsopy- 

 gaster in having more developed petals and less pointed bourrelets. 



Remarks. — This genus includes most of the Tertiary species that 

 Lambert and Thiery referred to their Procassidulus, except for 

 Twitchell's Cassidulus depressus, which Cooke (1959, p. 64) con- 

 siders a synonym of Eurhodia patellif ormis (Bouve), Desor's Cassid- 

 idus amygdala, which also appears to be a Eurhodia, and Kew's 

 Cassidulus mexicanus, which is a Rhyncholampas. Many of the 

 pre-Tertiary species that Lambert and Thiery refer to Procassidulus, 

 including the type species, have a tetrabasal apical system and should 

 be referred to Rhynchopygus. All the Tertiary species that they refer 

 to Rhynchopygus, except R. dyasteroides Duncan, have monobasal 

 apical systems and should be referred to Cassidulus. Cooke (i959) 

 pp. 56-59) refers four species to Cassididus (Cassidulus), but three 

 of them, C. sabistonenis Kellum, C. gouldii (Bouve), and C. ericsoni 

 Fischer, are very large, have well-developed phyllodes, and probably 



