STOMOPNEUSTID^E. 229 



STOMOPNEUSTID^ Mortensen. 

 Plate 90, figs. 11, 12. 



To Mortensen (1903, '^ngolf" Ech., pt. 1, p. 133) belongs the credit of 

 separating Stomopneustes from tlie other regular Echini and placing it in a 

 family by itself. While his reasons for so doing seerh quite trivial, the exami- 

 nation of the internal anatomy reveals the soundness of his conclusion and 

 strongly suggests that where the pedicellaria) and spicules of a sea-urchin show 

 really important characters, there will be found morphological characters of 

 real significance. And the corollary would naturally follow that if the careful 

 study of an echinoid fails to reveal characters in the test or the internal anatomy, 

 of real morphological value, whatever differences the spines, pedicellariae, and 

 spicules may show, however interesting they may be, are not significant and have 

 little bearing on a natural classification. 



The alimentary canal of Stomopneustes is very long and much looped, as in 

 the Centrechinidse. Its most noticeable pecuUarities are the short oesophagus, 

 and the very large intestinal appendage. The lantern shows at once how dis- 

 tinct from either the Echinidse or Echinometridse, Stomopneustes is, for the 

 epiphyses are relatively small and do not arch over the foramen, as they do in 

 those families. The teeth are however strongly keeled. The general appearance 

 of the lantern and teeth is very similar to that of Glyptocidaris crenularis (PI. 90, 

 figs. 3, 4) and shows that the family undoubtedly belongs in the suborder 

 Stirodonta Jackson. The auricles in Stomopneustes are only moderately 

 developed, meeting but hardly fusing, in an arch. 



The test is essentially similar to what is found in the Echinidse. The outline 

 of the ambitus is typically circular, but there seems to be a slight tendency to 

 elongation of one axis. The M. C. Z. collection contains a specimen 69 mm. 

 measured through interradius 2 and ambulacrum V, but only G7 mm. at right 

 angles to that line. Another specimen is 59 mm. through ambulacrum III and 

 interambulacrum 5, but only 57 mm. at right angles to that line. In both of 

 these specimens, the test is somewhat asjmimetrical and the elongation may be 

 pathological and not normal. The primary interambulacral plates are resorbed. 

 The primary ambulacral (buccal) plates carry numerous pedicellaria^ and some 

 small spines. Scattered in the buccal membrane are a number of small plates, 

 some of which, at least, carry pedicellariae. The ambulacra are remarkable 

 for the excessive development of certain primary tubercles. Seen from the inside, 



