INVERTEBRATE ANIMALS. I 567 



of new Cystideans from the Lower Palaeozoic rocks of Bohemia. 

 Some valuable morphological observations are also recorded therein; 

 but most of them refer to questions of too complex a nature for 

 discussion here. One point, however, must be noticed. In the 

 new genus Aristocystites and in some half-dozen others Barrande 

 describes the calcareous plates of the test as covered by a smooth 

 1 external epidermis ' which completely closes the openings of the 

 pore-canals that penetrate the substance of the plates. This epider- 

 mis is very thin, not more than yJq part of an inch in Proteocystites, 

 and is therefore but rarely preserved to any great extent. The 

 pores are sometimes isolated (haplopores), or a pair may be linked 

 by a horse-shoe-shaped groove, or open together in a small oval 

 depression, the ' oscule,' the whole structure being commonly known 

 as a ' diplopore.' It was the resemblance of these diplopores to 

 the groups of twin ambulacral pores in the Ordovician Sea- Urchin 

 Bothriocidaris, which led Loven to point out that the old theory 

 of the connection of the diplopores of the Cystideans with the 

 ambulacral system might after all be correct. This view, however, 

 will have to be abandoned altogether if the pores really are closed by 

 the external epidermis in the manner described by Barrande. But 

 there is some doubt as to whether the appearances described by 

 him may not be capable of a different interpretation, more especially 

 as he suggests in one place that the pores may have been connected 

 with tube-feet like those of the Urchins, while in another he notices 

 their similarity to the respiratory pores of the Asterids which give 

 passage to the gills or papulse. But neither of these explanations 

 could be possible if the pores really are closed as he describes. 



" Neumayr, believing Miiller's classification of the Cystidea ac- 

 cording to the characters of their pores to be no longer a practica- 

 ble one, has recently proposed the following scheme, which may be 

 adopted until a fuller morphological knowledge of the group has 

 provided us with the materials for a better one. 



" I. Order Spieeronitid^e. — Test composed of numerous irregu- 

 larly disposed plates, which may be aporous or bear haplopores or 

 diplopores, but never rhombs. Five ambulacra, sometimes termi- 

 nating in feebly developed arms. Generally sessile, but sometimes 

 free or stalked. 



" Family 1. Spharonitintz. — Ambulacra superficial and branching. 

 Sphczronites, Glyptosphcerites, Fucystis, Proteocystites, Protocrinus. 



"Family 2. Aristocysti?i(E. Ambulacra subtegminal and branch- 

 ing. Aristocystites, Pyrocystites, Crater ma. 



" Family 3. Mesitince. Ambulacra superficial and simple. Mesites, 

 Agelacrinus, Fdrioaster, Cytaster, Hemicystites. 



" II. Order Echinospieeritid/e. — Test composed of numerous 

 rhombiferous plates ; often with only three ambulacra, and slightly 



