KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 25. N:0 2. 



149 



and Springers paper on the Perisoraic Plates (ja?n dt.). It is also seen in specimen a 

 (tig. 252). Tlie plates of the tegmen are extremely irregular and differ in each of these 

 lo ur specimens. There may, however, be noted in specimen o, o large smooth plates, inter- 

 radial in position, which occupy the central part of the tegmen. The posterior of these 

 is larger than the others, and forms together with the right and left anterior plates a 

 central triradiate suture; thus it separates the right and left posterior plates from one an- 

 other. Around these 5 large plates are a number of plates, which on the whole are much 

 smaller, but which varv much in size among themselves. They may be divided into two 

 sets, — ambulacral and interambulacral. The ambulacral series consist in the main of 

 larger plates than those lying between theni; and of the ambulacral plates themselves 

 those nearer to the actinal centre are far larger than the abcentral ones, so that in eaeh 

 of the rays on the right side, at all events, the plate next to the large interradial and 

 central plate nearly equals it in size. The plates of the ambulacral series are of course 



specimen b. specimen c. 



Text-tig. 20. Cyathocrinus ramosus, tegmina, X 3 diam. 



specimen h. 



nothing more than covering-plates, and as such alternate with each other. They are, 

 however, somewhat irregular and include other quite minute plates irregularly distributed 

 among them. Among the interambulacral plates there can be distinguished, except in the 

 posterior interradius, a plate, generally rather larger than the others, resting on the radial 

 processes. Turning now to specimen b, \ve notc the same large postero-central plate; but 

 instead of this meeting 4 other plates, it meets 7 or 8 plates, the larger of which are 

 radial rather than interradial in position; in other words they appear to follow fairly 

 regularly on the ambulacral series. The remaining tegminal plates are not well preserved, 

 and one cannot clearly distinguish any particular plates as resting on the radial processes. 

 In specimen h one can hardly distinguish even the postero-central plate, while the other 

 central plates are split up, and both they and the covering-plates are separated by a 

 number of small irregular plates. In specimen a (lig. 252) although the central plates 

 are of larger size than the others, they have no definite arrangement. In none of these 

 specimens can any plate be pointed to as perforate or as specially folded. 



