The Echinoid Directory

Sismondia Desor, 1857, p. 225

[=Sismondaea Mayer-Eymar, 1897, p. 2]

Diagnostic Features	Small, ovate to subpentagonal in outline with rounded ambitus. Oral surface sunken towards peristome. Apical disc central with four gonopores. Hydropores in a groove. Petals open distally; weakly bowed. Ambulacral zones much wider than interambulacral zones at ambitus. Peristome central; small and circular. No food grooves. Periproct opening on oral surface towards posterior margin; at contact between the first and second paired post-basicoronal plates. Basicoronal interambulacral plates projecting slightly beyond first paired ambulacral plates. Paired ambulacral plates pointed and projecting perradially. Second paired ambulacral plates not enlarged. Tubercles on oral surface small and dense with sunken areoles. Ten radial partitions with lateral outgrowths forming incipient concentric laminae.
Distribution	Middle Eocene to Lower Miocene, Europe, Africa, Middle East, Asia, Japan, Australia.
Name gender	feminine
Type	Scutella occitana Defrance 1827, p. 231, by subsequent designation of Pomel, 1883, p. 72.
Species Included	S. convexa Nisiyama, 1937; Aquitanian, Lower Miocene, Bonin Islands. S. javana Gerth, 1922; Lower Miocene western Pacific. S. polymorpha Duncan & Sladen, 1884; Eocene, Somalia, India. S. occitana (Defrance); Late Eocene, France. S. murravica Tate; Lower Miocene, Australia. Numerous other fossil species have been named but require restudy to confirm their taxonomic placement.
Classification and/or Status	Clypeasteroida, Scutellina, Laganiformes; Laganididae (?stemgroup). Presumably paraphyletic by exclusion of more derived Laganinae and possibly Neolaganinae.
Remarks	Differs from other members of the Laganidae in having relatively simple internal butressing. In Sismondia there are 10 radial struts which have three to five short lateral branches that form incipient cicumferential partitions. In other genera the circumferential partitions are well developed. Also the basicoronal ambulacral plates are less pointed perradially than in other taxa. J. W. Durham 1955. Classification of clypeasteroid echinoids. University of California Publications in Geological Sciences 31(4), 73-198. Mortensen, T. 1948. A Monograph of the Echinoidea IV.2 Clypeasteroida. C. A. Reitzel, Copenhagen. Nisiyama, S. 1968. The echinoid fauna from Japan and adjacent regions part II. Palaeontological Society of Japan Special Papers 13, 1-491, pls 1-30.