CARBONIFEROUS FOSSILS OF IRELAND. 171 



Sabella antiqua. MCoy. (PI. IV. fig. 11). 



Sp. Ch. — Tube composed of very fine grains, cylindrical for about one incli and a half, gradually 

 tapering at one end ; diameter of tube about one line. 



This curious fossil occurs in considerable numbers in the shales of several districts in Ireland. When 

 the specimens are well preserved, they shew the finely granular, arenaceous tube, with, in many instances, its 

 smooth, glossy, membranous lining ; the specimens are usually more or less curved, particularly towards the 

 smaller end. They are usually about two or two and a half inches long. 



ECHINODERMATA. 



The Echinodermata are the most highly organized of the Nematoneura, and form an exceedingly well-de- 

 fined group. 



Some of them, as the SipuncuUdcB, resemble worms in their external appearance, being cylindrical, soft, 

 and without feet ; their internal structure, however, is perfectly that of the Echinodermata. Next come the 

 Holothiirice, which, though still without a calcareous covering, approach very nearly in structure to the Echin<e; 

 they are for the most part oval and smooth, with five rows of ambulacra, or rows of tubular suckers or feet (some- 

 times scattered over the body) the head is surrounded with beautifully pinnate, leaf-like gills. The Echini differ 

 from those in having the entire body enclosed in a hard, calcareous, spheroidal case, having five narrow ambu- 

 lacra, each composed of two rows of small, pentagonal plates, each plate perforated for the passage of two sets of 

 tubular, foot-like suckers ; between the ambulacra are five broader spaces, each composed of two rows of large, 

 pentagonal, imperforate plates, closely set with sharp spines, which both serve as a defence and assist in locomo- 

 tion; the mouth is furnished with a complex and powerful dental apparatus, which does not occur in any of the 

 other Echinoderms. The respiration is principally effected by tlie admission of water to the interior, where it 

 is made to pass in currents over the lining membrane of the shell and the surface of the intestines, by means of 

 the cilia with which they are covered. Following them, we have the AsteriadcE or star fishes, in which the 

 general form is depressed and divided into five or more rays, the under side of each of which is hollowed into an 

 ambulacral groove, analogous to the ambulacra of the Echinidce, and pierced for the passage of similar foot-like 

 suckers ; the tip of each ray exhibits a small red point, which is considered by Ehrenberg to be a true eye. 

 The external integument is coriaceous and covered with hard, calcareous granules, plates, or spines ; the mouth is 

 central and without teeth. By means of the genus Comatula we pass at once from the AsteriadcE to the Criiioidea, 

 which form the lowest group of the Echinodermata. 



Pal^chinus. Scouler. MSS. 



Gen. Ch. — Spheroidal; ambulacra composed of two rows of pentagonal plates, each perforated by two rows 

 of pores; anambulacra composed of two rows of pentagonal, and three or more rows of hexagonal plates; plates 

 covered with spiniforra tubercles, destitute of central ligament ; anus dorsal, central ; ovarian plates as in 

 Echinus; mouth ventral, central. 



The above name was provisionally given by Dr. Scouler to a specimen in the Collection of the Royal 

 Dublin Society, and to another in the Collection of the Rev. Mr. Fox ; they were exhibited at a meeting of 

 the Geological Society of Dublin under those names ; at that time the specimens were obscured by adhering 

 matrix, and considered unique ; a satisfactory examination was, therefore, impossible, and in consequence no 

 characters could be given to separate them from the other recent or fossil genera; the accession of additional 



