EEPORT ON THE CRINOIDEA. 299 



recent types that when allowance is made for the different stac^es of trpowth the 

 characters of the stem are of much use in the distinction of species. This is especially 

 the case if the number of internodal joints can be ascertained, which is not often possible, 

 however, with fossil stems. But I am more disposed than I formerly was to accept 

 the numerous species described by de Loriol and Quenstedt on the characters of the stem 

 alone. Under these circumstances it is possible that more of the Continental species 

 may eventually be found to occur in Britain, the number at present known beino- very 

 small. 



The geological range of individual species, both of Pentacrinus and of Extracrinus, 

 seems to be rather limited, no species occurring in all three divisions of the Lias. Out of 

 fifteen species of Pentacrinus which are found in the Middle and Upper Lias of Britain, 

 only two are common to the two horizons. Neither of the two Lower Lias species reach 

 the Middle Lias, though Pentacrinus hasaltiformis does so on the Continent. This and 

 Pentacrinus psilonoti are the only Continental species which have yet been recognised in 

 the British Lias. One species of the Kimmeridgve Clay, Pentacrinus sigmaringensis, also 

 occurs in the White Jura of the Continent. 



This agrees very well with the geographical distribution of the Pentacrinidfe in the 

 recent seas, the four West Indian species, though abundant in the Caribbean Sea, not 

 occurring elsewdiere ; while the remaining tw^o Atlantic species have respectively been found 

 at one and at three stations only. Pentacrinus naresianus was obtained in the West 

 Pacific in lat. 29° 55' S., and also in lat. 4° 33' N. (or possibly 9° 26' K), and has the 

 widest geographical range of any Pentacrinus, recent or fossil, that I am acquainted with. 

 Like the Silurian Crinoids, therefore, the species of Pentacrinus, both recent and fossil, 

 seem to be somewhat limited in their geographical range. 



The genus has, however, a wider geographical range than Metacrinus, wliich is 

 confined to the Pacific Ocean and the East Indian Archipelago. On the other hand, 

 while fourteen species of Metacrinus are known, Pentacrinus is only represented by eiglit, 

 together with the doubtful form which I have called Pentacrinus (?) mollis (PL XXXIIL 

 figs. 7-10). The mutual relationships of these eight species are shown in the 

 following table ; and it will be seen that they fall into two very natural groups, 

 which have the four Caribbean and the two Pacific species equally divided between 

 them. 



