from the Island of Malta. 81 



to the Bristol Institution ; we possess one, through the kindness 

 of M. Michelin, from the celebrated Urchin bed of Balistro (Cor- 

 sica) ; it is found likewise in the " Molasse du Cap Couronne pres 

 Martigues." (Michelin.} 



Family SPATANOID^E. 



The general outline of the Urchins of this family is oval, ob- 

 long or cordiform, and they satisfactorily exhibit the bilateral 

 symmetry of the Echinida. The mouth is anterior, bilabiate, 

 and edentulous. The anal opening is posterior and supramar- 

 ginul, and is closed by a complicated series of small plates. The 

 apices of the ambulacral areas are united at the summit of the 

 test. The anterior single ambulacrum has a different structure 

 from the antero- and postero-lateral pairs, and is in general lodged 

 in a depression of the test, which extends to the anterior border 

 forming the anteal sulcus; the test is extremely thin, and is 

 covered with small tubercles which support hair-like spines; 

 besides these there are some larger crenulated and perforated 

 tubercles which support large spines. There are two or four genital 

 pores which are sometimes placed close together, but are in other 

 genera apart. The eye-plates are five in number, and are placed 

 at the apices of the ambulacra in a pentagonal form around the 

 genital plates. We observe on the surface of the test of some Spa- 

 tangida, certain delicate lines called fascioles, having a smoother 

 appearance than the tubercular surface of the test ; they are fur- 

 rows which are strewed with microscopic tubercles destined to 

 carry very delicate spines, which, when seen under the micro- 

 scope, appear to have the same structure as the Pedicellaria. The 

 fascioles have a different disposition in each genus, and afford a 

 good character in giving definitions of the same ; when the 

 fasciole surrounds the ambulacral petals like an undulating 

 groove, as in Hemiaster, Schizaster, &c., it is said to be a peri- 

 petal ; when it surrounds the single ambulacrum, as in Amphi- 

 detus, it is internal ; when it extends along the sides, as in Schi- 

 zaster, it is lateral ; when it surrounds the circumference of the 

 test, as in Pericosmus, it is marginal ; when it is limited to the 

 base of the anal opening, it is subanaL We find sometimes in 

 the same genus more fascioles than one ; thus the subanal and 

 peripetal are frequently associated together. 



Genus SPATANGUS (Klein, 1734). 



Urchins, in general large with a thin test, a convex dorsal sur- 

 face, and the antero-lateral and postero-lateral ambulacral areas 

 composed of larger petals than in other Spatangida. The ante- 



