l80 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I44 



Range and distribution. — Paleocene to Recent, of worldwide dis- 

 tribution. There are many species from the Cenozoic of eastern 

 United States which Cooke has referred to Plagiopygus (which he 

 considers a subgenus of Cassidulus) or Cassidulus (Cassidulus), 

 which probably should be referred to RhyncJiolampas, including R. 

 sabistonensis Kellum, R. gouldii (Bouve), R. ericsoni (Conrad), 

 R. alabamensis (Twitchell), and R. georgiensis (Twitchell). Kew's 

 west coast species Cassidulus (Rhynchopygus) mexicanus is very 

 large, with well-developed broad lanceolate petals, and should be 

 referred to RhyncJiolampas. Unfortunately, on the holotype, and 

 evidently the only specimen known of this species, the adoral surface 

 is destroyed and nothing is known of the phyllodes. A photograph 

 of the adapical surface is included herein on plate 29, figure 4. This 

 species is quite similar to R. evcrgladensis (Mansfield) from south- 

 eastern United States, also from the Late Miocene of Florida, Its 

 phyllodes are probably similar to the very well developed phyllodes 

 in R. evcrgladensis. 



DESCRIPTION OF TYPE SPECIES 



RHYNCHOLAMPAS PACIFICUS (A. Agassiz) 



Plate 27, figures 5-8; plate 28, figures 1-3; text figures 154-159 



Pygorhynchus pacificus A. Agassiz, 1863. Bull. Mus. Comp. Zool., vol. i, p. 27. 



Remarks. — Mortensen (1948, p. 210) gives a very thorough de- 

 scription of this species, and it is not necessary to redescribe it here, 

 but new photographs are included. Although there are only four 

 specimens in the collections of the U. S. National Museum, they vary 

 in size from 8.5 to 55 mm. and exhibit some interesting ontogenetic 

 changes described below. The smallest specimen is the smallest that 

 has ever been described. 



ONTOGENY 



Apical system. — On the smallest specimen (text fig, 159), 8.5 mm. 

 long, there are no genital pores, but four gonoducts are visible on 

 the inside of the test in interambulacra i, 2, 3, and 4, near the apical 

 system. There are approximately 11 madreporic pores, and only i 

 tubercle. There are still no genital pores in the specimen 21 mm. long 

 (text fig. 158), but there are many more tubercles and madreporic 

 pores. In the specimen 35 mm. long (text fig, 157), genital pores 

 are present. 



