296 THE VOYAGE OF H.M.S. CHALLENGER. 



terminates below iu a nodal joint owing to its separation at the syzygy, as is the case 

 with so many fossil as well as recent Pentacrinidse. Although therefore it seems 

 tolerably certain that cirrus-verticils may occur in some species of Encrinus, the other 

 characters of many of the stem-fragments from the Muschelkalk render it equally certain 

 that Pentacrinus or an allied genus existed in the same seas as Encrinus. This has long- 

 been admitted in the case of the St. Cassian beds, which are considerably above the 

 horizon of the Muschelkalk ; and they have yielded to Laube ^ five varieties of Penta- 

 crmws-stems, which he has temporarily referred to as many species. Associated with 

 these he found one calyx which appears to belong to Pentacrinus; but it was too 

 imperfectly preserved for a definite opinion to be foi-med upon this point. 



All these eai'lier forms seem to belong to the section of the genus which was desig- 

 nated " Basaltiformes " by Quenstedt, after one of Miller's species with a pentagonal stem. 

 Essentially similar stems are found all through the remaining secondary rocks from the 

 Lias upwards, in the Nummulitic Limestones of Biarritz and Kreissenberg, in the London 

 Clay, and in the Italian Tertiaries. The calyces associated with them have a monocyclic 

 base, and bear simple or dichotomous arms, the two limbs of each fork being of equal 

 value, just as in the recent forms. Quenstedt's other two groups, the Briariden and the 

 Subangularen, are those to which the generic name Extracrimos was applied by the 

 Messrs. Austin. The type is limited in Europe to the Lias and Lower Oolites. Extra- 

 crinus briareus appears to occur in the lowest " quick ledge " at Lyme Regis, which 

 corresponds to Quenstedt's lowest bed a; but the t3rpe does not reach into the Middle 

 Lias, nor indeed into the upper beds of the Lower Lias. In the Jura, however, Extra- 

 crinus briareus has not been found below the Marlstone (Lias 7 and S); but it ranges up 

 through the Posidonia-heds, and is said to occur in the Lower Oolites. 



The range of the Subangularen is more limited. They do not occur in the Lower 

 Lias of either England or Germany, nor do they reach the top of the Posidonia-heds. 

 Many varieties have been made of lioth species, especially by Quenstedt ; Ijut it is note- 

 worthy that neither species occurs in all the three divisions of the Lias, Extracrinus 

 briareus being limited to one only, at any rate in this country. 



Those who have recognised Extracrinus as a genus, as, for example, Mr. E. 

 Etheridge,^ F.R.S., have usually regarded it as limited to the Lias. The Messrs. Austin, 

 however, speak of Extracrinus briareus as occurring in the Cornbrash at Kingscote Turn- 

 pike. They are certainly wrong about the species, l)ut I am very strongly inclined to 

 believe that they are correct as regards the genus, and also that the occurrence of the 

 Briariden in the Brown Jura (Inferior Oolite), as mentioned by Quenstedt,^ is not 

 unlikely. 



> Die Fauna cler Schichten von St. Cassian, Denlcschr. d. k. Akad. d. TFiss. Wicn., Bd. xx., xxiv., pp. 267-278. 

 - See his Presidential Address to the Geological Society, Quart. Journ. Geol. Soc, 1882, p. 147 (of separate cop}-). 

 ^ Encriniden, p. 270. 



