260 SPATANGIDyE. 



Locality and Stratij^rapJdcal Position. — It was collected from the Upper Greensand 

 near Lyme Regis, where it appears to be very rare, as I have seen only one 

 other English example in addition to Sir Henry De la Beche's gift to the British 

 Museum. In France it is found not unfrequently in the Micaceous Sandstone, I'etage 

 Cenomanien of Mans, Sarthe, and in the Gres Calcarifere (Cenomauien), of Fouras, 

 Charente-Inferieure. 



Family 11. — CLYPEASTERiDiE, WriffJit, 1856. (Not yet found in British Cretaceous 



strata.) 



Family 12. — Spatangid^, d'Orbiyny, 1853. 



The general outline of the urchins of this family is oval, oblong, or cordiform, and 

 they satisfactorily exhibit the bilateral symmetry of the Echinidse. Tbe mouth is 

 anterior, bilabiate, and edentulous. The anal opening is posterior and supramarginal, 

 and closed by a complicated series of small periproctal plates. The arabulacral areas are 

 united at the summit of the test. The anterior single ambulacrum has a different 

 structure from the antero- and postero-lateral pau's, and is lodged in a depression 

 of the test, which extends to the anterior border and forms the anteal sulcus ; the 

 test is extremely thin, and covered with small perforated tubercles, which support 

 hair-like spines ; besides these there are some larger crenulated and perforated tuljercles, 

 which support large spines. There are two or four genital pores, which are some- 

 times placed close together, but in other genera are apart. The eye-plates are five 

 in number, and placed in a pentagonal form at the apices of the ambulacra around 

 the genital plates. We observe on the surface of the test of some Spatangidse certain 

 delicate lines called fascioles, having a smoother appearance than the tubercular sur- 

 face of the test ; they are furrows which are strewed with microscopic tubercles 

 destined to carry very delicate spines which, when seeu under the microscope, appear 

 to have a structure similar to the Pedicellarise. The fascioles have a different dispo- 

 sition in each genus, and afford a good generic character in giving definitions of the 

 same ; when the fascicle surrounds the ambulacral petals like an undulating groove, 

 as in Hemiaster, Schizaster, &c., it is said to be peripetalous ; when it surrounds the 

 single ambulacrum, as in Jmpkidetus, it is internal ; when it extends along the sides, as 

 in ScJiizaster, it is lateral ; when it encircles the circumference of the test, as in 

 Pericosmtis, it is marginal; when it is limited to the base of the anal opening it is 



