SALENTD.E. 51 



between the two columns of large tubercles. They nre attached, in a more 

 or less pendant condition, by very short stalks, to minute tubercles on the 

 surface of the test. They are spheroidal in Salenia, but are usually ovoid 

 or ellipsoidal in Salenocidaris. In all the recent species the sphoeridia are 

 attached flush with the test and not in any depression or concavity, but in 

 the Upper Cretaceous Goniophorus, what are apparently deep pits for the 

 sphaeridia, like those of Coelopleurus, are present in the actinal part of the 

 ambulacra. 



The calcareous particles or spicules of the Salenidoe (Pis. 45, figs. 9, 20 ; 

 46, fig. 7) are curved rods and perforated plates with more or less numerous 

 and conspicuous projections. They exhibit great diversity, both in abun- 

 dance and in size and degree of development. In their simplest form the 

 curved rods have projections only on the convex side, but later (or in more 

 developed examples) the projections are found on both sides. As these pro- 

 jections increase in length and thickness, they anastomose more or less freely, 

 and very irregular, perforated plates are thus built up. The simplest rods 

 occur in the pedicels, especially near the tips of the abactinal ones, while 

 the most fully formed plates are found in the buccal membrane. Apparently 

 the abundance and complexity of the calcareous particles increase with age. 

 The slight differences noted between the species do not seem to be suffi- 

 ciently tangible or constant to warrant their use as a specific character. 



The general arrangement of the internal organs of the SalenidaB is shown 

 in figs. 3-6, PI. 43. The reproductive organs consist of short, dense tufts 

 of tubules, apparently confined to the abactinal part of the test and body- 

 cavity. The oesophagus is short and nearly straight. The stomach-intestine 

 is only of moderate length, but shows the usual undulations. Its arrange- 

 ment, however, is quite different in Salenocidaris from what it is in Salenia, 

 as shown by the examination of a number of specimens of each genus. In 

 Salenia (figs. 3, 4.), the lower or actinal half of the stomach-intestine is dis- 

 tinctly undulated, raised in the ambulacra, lowered in the interambulacra, 

 while the upper or abactinal half is much longer and narrower, and is nearly 

 cylindrical ; it is also greatly undulated, the interambulacral loops being 

 particularly well marked. In Salenocidaris (figs. 5, 6), on the other hand, 

 the undulations of the actinal half of the canal are scarcely visible, while 

 the abactinal half is much shorter and stouter than in Salenia, with only the 

 undulations of the posterior interambulacra marked, and at least two of 

 these modified into small pouches. 



