214 HAWAIIAN AND OTHER PACIFIC ECHINI. 



of the extinct species reveals the needlessness of the Pedinidae, it may be better 

 to leave the genus Csenopedina in that family. In any case, it certainly belongs 

 in the suborder Aulodonta Jackson. 



The species of Csenopedina agree in having a large abactinal system, nearly 

 or quite equal to half the diameter of the test; the ambulacral primary tubercles 

 are continued well above the ambitus; and secondary tubercles are more or less 

 numerous. In other particulars they are much like Pseudopedina Cotteau, to 

 which genus they are perhaps more nearly allied than to the true Hemipedinas. 

 They cannot properly be referred to Pseudopedina however and therefore 

 Mortensen's revival of the name Csenopedina, under which the type-species 

 (cubensis) was originally described, may be accepted, without however agreeing 

 with him that recent species cannot well be referred to genera known originally 

 only as fossils. 



Having already showed the close resemblance of Caenopedina to Centro- 

 stephanus, it will be unnecessary to repeat the various structural features of the 

 genus, but some of the details regarding which little has been published, may be 

 briefly referred to here. 



The most striking feature of the internal anatomy is seen in the brevity of 

 the upper coil of the intestine, which, unlike that of Echinothrix and the other 

 Diadematidse, almost wholly lacks the interradial loops and follows a very short 

 course near the abactinal surface of the test (PI. 90, fig. 2). The lantern and 

 teeth (PI. 90, figs. 3, 4) are like those of the Centrechinidse in every detail, but the 

 perignathic girdle is less developed than is the rule in that family; the auricles 

 are slender and do not quite meet over the ambulacra. Rudimentary Stewart's 

 organs can be easily distinguished. The characters of the test, and other ex- 

 ternal features, are so well known we need only mention them here. The 

 ambulacra are typically centrechinoid, while the primary tubercles of both areas 

 are equally so. The tubercles are high and without a trace of crenulation and 

 the areolse are very little or not at all sunken. The abactinal system is very 

 large, with a big periproct and small ocular plates. There is no trace of an anal 

 tube. The actinostome is well plated, especially in the ambulacra, as in the 

 Centrechinidse, and the buccal plates carry spines as in Centrostephanus. 



