The Echinoid Directory

• Test ovate without anterior sulcus. Ambitus rounded.
• Apical disc ethmolytic, with 4 gonopores.
• Anterior ambulacrum narrow and flush; pore-pairs small, rudimentary isopores.
• Other ambulacra narrow and sunken, the anterior pair almost at 180 degrees.
• Posterior petals only weakly divergent. Pore-pairs of inner (adaxial) series much reduced adapically compared to those in outer column.
• Periproct towards top of vertical truncate face.
• Peristome wider than long; kidney-shaped.
• Labral plate very short and wide; not extending beyond ambulacral plate 1.
• Plastron parallel-sided with curved suture between 2a, 2b and 3a, 3b. Plates 3a, 3b tapering posteriorly.
• Interambulacra 1 and 4 apparently not reaching the peristome.
• Spines and tubercles within peripetalous fasciole not enlarged.
• Well-developed subanal fasciole and peripetalous faciole. Subanal fasciole shield-shaped and with anal branches.

Early Miocene to Recent, Indo-Pacific, North Atlantic.

Rhynobrissus pyramidalis Agassiz, 1872, p. 58, by original designation.

• R. cuneus Cooke, 1957; Recent, North Carolina.
• R. hemiasteroides Agassiz, 1879; Recent, Tahiti, Hawaii, Australia.
• R. daviesi (Jain, 2002); Early Miocene, NW India.
• R. placopetalus Agassiz & Clark, 1907; Recent, Hawaiian Islands.
• R. pyramidalis Agassiz, 1872; Recent, China, Thailand, Singapore, India.
• R. tumulus McNamara, 1982; Recent, Australia.

Spatangoida, Micrasterina, Brissidae.

Monophyletic.

Very close to Rhabdobrissus, but differing in lacking primary tubercles inside the peripetalous fasciole.

The genus is discussed in detail by McNamara (1982).

Agassiz, A. 1872. Bulletin of the Museum of Comparative Zoology, Harvard College 3, p. 58

McNamara, K.J. 1982. A new species of the echinoid Rhynobrissus (Spatangoida: Brissidae) from North-West Australia. Records of the Western Australia Museum 9, 349-360.