880 Prof. S. Lovdn 07i the Structure of the Echinoidea. 



Of the living Spatangidse, by far the greatest number have 

 the four paired ambulacra like each other in closing with 

 petala towards the vertex, whilst the unpaired anterior ambu- 

 lacrum has its peculiar structure, and in one genus, Echino- 

 cardium^ even the alternation of entire and half plates, which 

 does not occur elsewhere in this family. Not more than two 

 genera can be found which form an exception to this : one of 

 them is Ltssonotus fragiUs, A. Agass., from the great depths 

 between Cuba and Florida ; the other was discovered by 

 Smitt and Ljungman during the expedition of the corvette 

 ^ Josephine ' in the year 1869, off Villa Franca, in the Azores^ 

 at a depth of 200-300 fathoms. A resemblance which this- 

 Spatangid presents at the first glance from above to certain 

 forms of Ananchytes ovata^ leads us to name it Palmotropus ; 

 the species may be called P. JosepMnce. All five ambulacra 

 lie in the plane of the test, without the slightest depression^ 

 and are apetalous ; so that they all finish similarly towards the 

 vertex — in this way, that their five or six youngest plates form a 

 simple and narrow row, such as we see nowhere else, in wliich^ 

 however, the alternating position of the pores indicates to 

 which side each plate is to be referred. The rows of the 

 trivium agree completely ; the unpaired one is not depressed, 

 and the dorsal arching of the test is uniformly within the 

 obovate circumference. These characters differ greatly from 

 those of the living Spatangidse ; others agree with them. The 

 mouth has a projecting lobe, and the somewhat depressed 

 posterior end of the test an infraanal fasciola. The genital 

 apertiires are two in number, corresponding to the posterior 

 paired interradia 1 and 4. The eye-plates are very distinct • 

 but the vertical plates cannot be distinguished ; the right 

 anterior one, however, has a bounded, irregular orifice, which 

 is the madreporite. The length of the animal described is 

 11'7 millims., and its breadth 9'1 millims. The presence of a 

 fasciola and a developed labrum unites Palcwtrojpus with the 

 SpatangidcB, if we exclude from their character the petala and 

 the difference of the unpaired frontal ambulacrum from the rest. 



There is no living Spatangid destitute of tentacular pores in 

 any of the plates of the frontal ambulacrum. In all, its 

 oldest ventral plates, within the buccal area, are like those of 

 the other ambulacra; and the younger ones, situated nearer the 

 vertex, have more or less distinct double pores, the elongated 

 apertures being closed in the middle by a portion growing out 

 from the margins. 



Because the Spatangidre in general do not grow to an equal 

 extent in the different radii, but most frequently more in the 

 direction of the bivium than of the trivium, their ambu- 



