IN THE MORPHOLOaT OF THE CYSTIDEA. 25 



comme JEchinoencrinus SenJcenlergi, Von Buch." It is obvious, 

 however, that these ramifying lines indicate the positions of the 

 ambulacra diverging from a central peristome, aud that the five 

 compartments which they enclose represent the five interambu- 

 lacral areas on the disk of a Neocrinoid, the larger one being that 

 of the anal interradius. It was probably pierced by the rectum, 

 as in the recent forms, and the whole disk of Ascocystis, with its 

 ambulacra dividing to supply the numerous appendages round its 

 edge, bears a singular resemblance to that of a Metacrinus such as 

 M. nobilis * and M. rotundus t, in which the pinnule-ambulacra 

 appear on the disk. In the Pentacrinidte, too, the peristome and 

 the bases of the ambulacra are roofed in by covering-plates with- 

 out any distinct traces of orals, just as in many Cystids. 



The presence of an oral pyramid consisting of five plates in the 

 form which Barrande called Pyrocystis desiderata J is a point of 

 some importance, as it conclusively settles the nature of the 

 structures which he called " hydrophores palmes." They are 

 well shown in his figure of the interior of the test of this type 

 (Pi. I. fig. 10) ; while that of the exterior shows their relation to 

 the oral plates, which suggests at once that they are subtegminal 

 ambulacra. This obvious explanation of them has already been 

 given by ]N"eumayr on quite difl'erent grounds § ; but it did not 

 find favour with the anonymous reviewer of Barrande's work in 

 ' IS ature,'who criticised it as follows || : — 



" Neumayr thinks that the opening which they surround is the mouth, and 

 that they are subtegminal ambulacral grooves. How this can be when their 

 distal ends are unconnected with the exterior is not easy to understand. Bar- 

 rande, moreover, cannot say whether they are at the oral or aboral pole. A 

 comparison of figs. 28 and 32 on pi. xxix. suggests that they are at the aboral 

 end, and that the large opening represents the axial canal of the stem. May 

 they not be connected with nerve-cords passing from a chambered organ? " 



The reviewer is no doubt right in assuming that the large ojDening 

 seen in fig. 28 is the axial canal of the stem ; but there is not 

 much resemblance between this and the low quinquepartite 

 pyramid of fig. 32 on the same plate, which, as shown in fig. 33 



* Zool. Chall. Exp., " Eeport on the Crinoidea," vol. xi. 1885, pi. xliii. fig, 3. 



t Trans. Linn. Soc. 1884, ser. 2, Zool. vol. ii. pi. 1. fig. 2. 



I Op. cit. pi. xxix. figs. 32, 33. 



§ ' Die Stilmme des Thierreiches,' Bd. i. 1889, p. 409. 



il ' Nature,' vol. xl. 1889, p. 269. 



