44 



ECHTNODERMS OF THE BRITISH ISLES 



by means of a more or less distinct, soft stalk. Often they are 

 collected in a large cushion round the base of the larger spines. 

 In living specimens these cushions generally rise to the point 

 of the spine, while in ])reserved specimens they are, as a rule, 

 retracted to the base of the spine. Straight pedicellaria? are often 

 found attached to the adambulacral spines. 



Special organs of another kind are the so-called " cribriform " 

 organs, peculiar to the family Porcellanasteridae (and Gonio- 



FiG. 26. — Various sorts of pedicellariae of Asteroids. 

 (From Danmark's Fauna.) 



1. Simple type (Pontaster tenuispinus). x 13. 2. Pectinate pedicellaria {Pseud- 

 archaster Parelii). x 13. 3. Paxilla-like groups of grains from the dorsal side of Ceramaster 

 granulans, with two valvate pedicellarise. x 13. 4. Bivalve pedicellaria of Hippast^ria 

 phrygiana. x G. 5. Crossed pedicellaria of Asterias rubens. x 120. 6. Valve of the 

 same, seen from the inside, x 120. 7. Group of straight pedicellaria on an adambu- 

 lacral spine of Asterias rubens ; the small, lowermost one just beginning to form, x 10. 

 p, Pedicellaria. 



pectinidse). These are parallel skin-folds, sometimes divided 

 into papillae, which are then serially arranged ; each fold is sup- 

 ported by some delicate calcareous plates. They are situated 

 between the marginal plates (Fig. 27), bounded on each side by 

 a series of scale-like papillae, like a web, which may (Ctenodiscus) 

 conceal the whole of the organ. In many forms there are very 

 fine spines in the furrows between the marginal plates, covered 

 by a thick, ciliated skin ; they may be designated fascioles. 

 These, as well as the cribriform organs, which are also strongly 



