. The Cambridge natural history. Zoology. SS6 ECHINODERMATA ECHINOIDEA petals, E. pennatifidum twelve to fourteen. Both come from deeper water than E. cordatum. Fam. 7. Brissidae.âAllied to the Spatangidae, but dis- tinguished by sunken petals and a peripetalous fasciole. Two genera are recorded from the British area, ScTiizaster and Bribsopsis, but the first has only been found once in deep , ⢠water; the second is common. Schizaster has the front petals three times as long as the hind ones, and no sub-anal fasciole. Brissopsis has the front and hind petals of about the same length, and a su
. The Cambridge natural history. Zoology. SS6 ECHINODERMATA ECHINOIDEA petals, E. pennatifidum twelve to fourteen. Both come from deeper water than E. cordatum. Fam. 7. Brissidae.âAllied to the Spatangidae, but dis- tinguished by sunken petals and a peripetalous fasciole. Two genera are recorded from the British area, ScTiizaster and Bribsopsis, but the first has only been found once in deep , ⢠water; the second is common. Schizaster has the front petals three times as long as the hind ones, and no sub-anal fasciole. Brissopsis has the front and hind petals of about the same length, and a sub - anal fasciole. The only British species is called B. lyrifera, on account of the fiddle- shaped outline of the peri- petalous fasciole. Hemiaster (Fig. 250) in Fig. shell of Schizaster, showing general resembles &/wMSfer, peripetalous fasciole. Anterior but the petals are equal in ambulacrum ; fasc, peripetalous fasciole : i . i j ii j. i_ â ;, genital pores, x 1. (Alter Agassiz.) length, and the two posterior serve as brood-pouches for the young. This genus is mainly Antarctic. Fossil Echinoidea.âEchinoidea are well represented in the geological record, and form a characteristic element in many fossil faunas. They appear in the Ordovician formation, but the first representatives of an existing family (Cidaridae) only appear in the Permian. Space will only permit us to treat of the extinct members of the group very briefly. Leaving out of sight the representatives of families still living, the fossil Echinoidea may be divided into two great groups, viz.:â (a) Palaeozoic forms, which in some points serve to connect the Endocyclica with the primitive Asteroidea. (&) Mesozoic forms, which serve to connect the Clypeastroidea and Spatangoidea with the Endocyclica. The Palaeozoic forms are often called Palaeoechinoidea, and they are above all distinguished by the fact that the number of. Please note that these images are extracted from scanne
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
