GENUS PLEURECHINUS, L. AGASSIZ. 449 



the species Opechinus percultus, Desor, from the tertiaries of 

 Java. 



With regard to the Echini described by D'Archiac and Haime in 

 ' Les Animaux f ossiles de I'lnde,' the tjrpes of which are in the 

 collection of the Geological Society, the condition of preserva- 

 tion is wretched ; and those distinguished naturalists, in order to 

 convey their meaning to their artist, inked the surface of the 

 tests. Hence every depression along the sutural lines seems to 

 be of great importance. Specimens of so-called Temnopleuridae 

 from the same geological horizon, now in course of description 

 and publication by Percy Sladen, F.Gr.S., and myself, indicate the 

 meaning of the multij)licity of depressions on the test. They are 

 the normal depressions (the so-called pits, but not true pits) along 

 the horizontal sutural lines of the test, and nothing more ; but 

 the ornamentation of the raised rib-like structure of the test, 

 which carries the principal tubercles and several rows of minute 

 ones, sometimes extends over the depression, and nearly or quite 

 unites with the corresponding ornamentation of the neighbouring 

 rib. When a specimen is slightly worn and inked, the impression 

 conveyed to the eye is that there were two or more smaller 

 depressions within the line of the normal large one. 



There are always four depressions along a horizontal line above 

 the ambitus in Temnopleurus, and normally there should be only 

 two ; but the two vertical rows of large primaries have their 

 base continued over the horizontal sutural depression, and four 

 dejiressions are formed. 



The genus Opechinus is valueless, as its essential character, 

 never generic, is due to the chances of growth of ornamentation. 



It is remarkable that Desor should write about the species of 

 Opecliinus, that there were living and fossil species, the first in- 

 habiting the tropical seas. Certainly no form like an Opechinus 

 has ever been seen in a perfect and good state of preservation. 

 It must be noticed also, that the type of L. Agassiz does not 

 warrant the statement that there are six pits in horizontal series. 



The next notice of the genus Fleurechinus is found in A. 

 Agassiz's magnificent Report on the Ecliini of the ' Challenger ' 

 Expedition (p. 108, pi. x". figs. 1, 2). Specimens of the species 

 hothryoides were obtained oiF Kobi, in Japan, in from 8 to 20 

 fathoms. 



The following is the description : — " The ' Challenger ' col- 

 lected three small specimens of a Temnopleurid, which I am 



