DE. P. n. CAUPENTEE ON SOME AECTIC COMATUL^. 59 



would present more embryonic characters than those oi A. prolixa. 

 This, however, is exactly contrary to the real state of the case. 

 Both the calyx and the arm-joints of yi. tenella exhibit characters 

 of greater maturity than equal-sized or even larger examples of 

 A. prolixa. Thus,' for example, in the large Atlantic variety of 

 A. tenella the radials are barely visible (PL IT. fig. 7) ; and they 

 are only traceable in younger individuals as a narrow band round 

 the edge of the ceutro-dorsal (fig. 6). But this is much broader 

 in tlie calyx of the nearly equal-sized but still immature A. prolixa 

 from the ' TegetthofF ' expedition (fig. 2) ; so that it presents an 

 appearance similar to that of the embryonic types A. abyssicola and 

 the genus Atelecrinus. Even in the larger ' Tegetthoff ' specimen, 

 which is of much greater size than any Antedon tenella I have ever 

 seen, a considerable portion of the radials appears externally, 

 and the full-grown A. prolixa from Jan Mayen (fig. 4) shows 

 more of them than the largest A. tenella of the ' Blake ' dredgings, 

 though the latter is absolutely of much smaller size (fig. 7). 



4. What has been said above concerning the radials holds 

 good also for the costals and lower brachials, which are relatively 

 longer and more embryonic in the immature A. frolixa thania 

 the largest and best-developed individuals of A. tenella. This 

 difference, however, is most apparent when the two young 

 specimens of A. prolixa from Jan Mayen are compared with 

 equal-sized examples of A. tenella from, the North Sea. Fischer 

 states that the former present all the characters which are given 

 by Diiben and Koren and later authors as characteristic of 

 A. Ba-^sii. But Diiben and Keren's description of this type is 

 over forty years old, and not of much value therefore for syste- 

 matic purposes at the present time, while subsequent writers 

 have added little of importance to it. A direct comparison of 

 Fischer's two specimens with typical examples of ^. tenella leads 

 to very different results. Their cirri are considerably larger than 

 those of a Scandinavian form of equal size which has well-developed 

 genital glands and all the other characters of maturity. Its radials 

 are almost entirely concealed, while in Fischer's specimens a 

 considerable portion of them is visible, as described above. Similar 

 differences appear between the lower brachials of the two forms, 

 as will be evident from a glance at figs. 3 and 5 on Plate II. 

 Those of the young A. prolixa are much elongated, and present 

 all the characters of immaturity ; while in the arm of A. tenella of 



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