14 



Von Buch on Crinoidea. 



and consequently of tentacula, is important. They reappear 

 on many Encrinites ; for instance, on Actocrinites, on Rho- 

 docrinites, and even on Marsupites. (Bronn, Lethzea, PL IV.) 

 The rhombs are not evident on the surface of Sphceronites 

 Pomum. Each plate bears a number of small systems, sepa- 

 rated inter se. Two pores are always connected with one 

 another, but these systems are scattered without arrangement 

 over the entire surface. This species has hitherto only been 

 found in Sweden. 



In the upper half of the Sphceronites, but still a fourth of the 

 sphere distant •from the mouth, there is a large pentagonal 

 aperture, which is closed by five triangular valves project- 

 ing in a flattened pyramid. Gyllenhahl and his successors 

 call this aperture the mouth. But analogy with the allied 

 forms requires the mouth to be above, and an aperture closing 

 exteriorly appears little adapted for a nutriment-receiving 

 mouth. Probably it is an oviduct. Above, quite close to the 

 mouth, and constantly to the right of the valvated aperture, 

 there is a third very small opening, penetrating deep into the 

 interior, probably an anus. A similar small anal aperture is 

 likewise evident between three laminae on Apiocrinites, where 

 hitherto it has not been observed, resembling the anus of the 

 living Comatula. Gyllenhahl expressly states, " I always found 

 this Sphceronites Pomum in Westgothland, at a greater depth 

 than Sphceronites Aurantium, and in far greater number." It 

 is therefore surprising that it has not yet been met with in 

 the neighbourhood of St. Petersburgh. 



Hemicosmites pyriformis. — By means of this beautiful and . 

 extremely elegant form, we approach a great step nearer to 

 the true Crinoidea. Although still without arms and closed, 

 there are already here but few plates or assulae, in definite num- 

 ber and regularly combined. The Hemicosmites is reverse 

 pear-shaped, and consists of three parts, of pelvis, thorax, and 

 vertex. The pelvis on the slender pentagonal petiole is formed 

 of four pieces, which are arranged in a hexagon. Two of them 

 are pentagons, the two others lozenges (rhombs). Six costals 

 in two different groups form the thorax. Three of these plates 

 are narrower, and above, between those on the left, there is 

 a pentagonal aperture closed with valves as in Sphceronites. 

 The three other assulae are broader, and the superior apex of 

 the elongated hexagon is somewhat truncated. In accordance 

 with this, the vertical plates arching over the whole also 

 divide into two groups; on the side of the broader assulae 

 there is on each truncation of their apex a longitudinal piece, 

 as it were, inserted, and there are therefore three such pieces ; 

 they are wanting on the side of the valvate aperture. The 

 exceedingly small laminae which cover the mouth on the top 



