No. 3.] ' GEOLOGY AND MINERALOGY. 345 



GEOLOGY AND MINERALOGY, 



On tue Structure or the Paleozoic Crinoids. — The 

 best known living representatives of the Echinoderm class Cri- 

 noidea are the genera Antedon and Pentacrinus — the former the 

 feather stars, tolerably common in all seas ; the latter the stalked 

 sea-lilies, whose only ascertained habitat, until lately, was the 

 deeper portion of the sea of the Antilles, whence they were rarely 

 recovered by being accidentally entangled on fishing-lines. With- 

 in the last few years Mr. Robert Damon, the well-known dealer 

 in natural history objects in "Weymouth, has procured a consider- 

 able number of specimens of the two West Indian Pentacrini, 

 and Dr. Carpenter and the author had an opportunity of making 

 very detailed observations both on the hard and the soft parts. 

 These observations will shortly be published. 



The genera Antedon and Pentacrinus resemble one another in 

 all essential particulars of internal structure. The great distinc- 

 tion between them is, that while Antedon swims freely in the water, 

 and anchors itself at will by means of a set of " dorsal cirri," 

 Pentacrinus is attached to a jointed stem, which is either perma- 

 nently fixed to some foreign body, or, as in the case of a fine 

 species procured off the coast of Portugal during the cruise of the 

 Porcupine in the summer of 1870, loosely rooted by a whorl of 

 terminal cirri in soft mud. Setting aside the stalk, in Antedon 

 and Pentacrinus the body consists of a rounded central disc and 

 ten or more pinnated arms. A ciliated groove runs along the 

 " oral " or " ventral " surface of the pinnules and arms, and these 

 tributary brachial grooves gradually coalescing, terminate in five 

 radial grooves, which end in an oral opening, usually subcentral, 

 sometimes very excentric. The oesophagus, stomach, and intes- 

 tine coil round a central axis, formed of dense connective tissue, 

 apparently continuous with the stroma of the ovary, and of invo- 

 lutions of the perivisceral membrane ; and the intestine ends in 

 an anal tube, which opens excentrically in one of the inter-radial 

 spaces, and usually projects considerably above the surface of the 

 disc. The contents of the stomach are found uniformly to consist 

 of a pulp composed of particles of organic matter, the shields of 

 diatoms, and the shells of minute foraminifera. The mode of 



