NO. 3 CASSIDULOID ECHINOIDS — KIER 179 



ambulacrum; buccal pores present; tubercles on adoral surface much 

 larger than on adapical, scrobicules large, bosses eccentric anterior ; 

 naked, often pitted area in interambulacrum 5, ambulacrum III. 



Comparison zvith other genera. — Rhyncholampas is distinguished 

 from Cassidulus by its larger test, broader, lanceolate petals, gen- 

 erally more posterior periproct, and more developed phyllodes with 

 more occluded pores. Although the type species of these two genera 

 are very distinct from one another, there are species which have 

 some of the characters of both and are difficult to place definitely in 

 one of them. 



Remarks. — Mortensen (1948, p. 202) incorrectly states that when 

 A. Agassiz established this genus he made Cassidulns carihoearum 

 the type species. Furthermore, Grant and Hertlein (1938, p. 107) 

 are mistaken in saying that C. carihoearum is the type species by 

 monotypy. Agassiz referred two species to his genus, C. carihoearum 

 and R. pacificits, but did not select a type species. Lambert and 

 Thiery designated R. pacificus. Mortensen says that even if R. 

 pacifictis were considered as the type species of Rhyncholampas, the 

 genus would still be a synonym of Cassidulus. He states that R. 

 pacificus has more developed phyllodes and that the pores in its petals 

 are more unequal, but suggests that these dififerences may be due to 

 the different size of the specimens examined, and that if specimens 

 of the same size were compared, these differences might be so small 

 as to be unimportant for a generic distinction. This argument would 

 be pertinent if the species C. carihoearum were based on immature 

 specimens, and R. pacificus on adults. Such is not the case. Many 

 specimens of C. carihoearum are known, and none are larger than 

 31 mm. in length. There is no evidence that these small specimens 

 are not adults. Fortunately, there are two small specimens of R. 

 pacificus in the U. S. National Museum, one 21 mm. long and the 

 other 35 mm., and these immature specimens are generically distinct 

 from C. carihoearum. A phyllode in the smallest specimen already 

 has three occluded pores (text fig. 154) in each half -ambulacrum, 

 whereas no occluded pores occur in specimens of the same size or 

 even larger of C. carihoearum. It is true that the pores in the petals 

 of the small specimen of R. pacificus are more equal, with the outer 

 pore less elongated (pi. 28, fig. i) than the outer pore in an adult. 

 However, the shape of the petals in R. pacificus is quite different 

 from the petals in C. carihoearum. In R. pacificus the petals are 

 lanceolate with more of a tendency to close distally. This difference 

 is evident even on the smallest specimen. 



