TEMNECHINUS. 7 



about sixteen primary tubercles, ranged in a regular row, in each half of an arabulacral seg- 

 ment. The mouth is rather small in proportion to the diameter, but is larger than the genital 

 disk. It is obscurely decagonal. The genital disk is very prominent. The five genital 

 plates are pentangular, very tumid, and steep-sided : then* sides quite smooth and 

 excavated ; their summits coarsely granulated, with two or three small secondary tubercles 

 on their inner edge, bordering the anus. The genital pores are at the projecting angles of 

 the plates, at their lowest and smoothest part. The eye plates are pentangular and smooth, 

 except in the centre. 



The dimensions of a fine specimen are |-i-ths of an inch in breadth by -j^^ths of an inch 

 in height. 



Spines apparently belonging to this species are short and stout, rapidly tapering, and 

 grooved by about twelve rather strong and deep sulcations. The neck of the spine is 

 surrounded by a ring of very strong crenulations. 



Fine specimens from the Coralline Crag of Ramsholt are contained in the cabinets of 

 Mr. Searles Wood, Mr. Charlesworth, and that of the Museum of Practical Geology. 



2. Temnechinus melo-cacttjs. Plate I, fig. 2. 



This species is equally beautiful with the last, from which it differs conspicuously in its 

 less depressed shape, the defined and not confluent sutural pits of its upper surface, the 

 sloping sides of the genital plates, and the more equal dimensions of the secondary 

 tubercles. 



Its general shape is a depressed, but not flattened or hollowed out spheroid, with 

 tumid but not bulging sides. The interambulacral segments are (centrally) to the 

 ambulacrals as 3 to 2. The sutural pits of their dorsal surfaces are strongly marked, but 

 not so deeply hollowed out as in T. excavatus. They alternate regularly, and are not 

 confluent, except very slightly so immediately near the apical disk. The pits preserve 

 their dimensions and arrangement centrolaterally, and only become oljsolete in the 

 immediate neighbourhood of the mouth. The interambulacral plates bear on their 

 elevated portions each a conspicuous and prominent, but not large, smooth, primarv 

 tubercle, smaller in proportion to the size of the plate, than those in the last species. It is 

 nearly surrounded by secondary tubercles and granules, rather scattered, and most of the 

 former nearly equal in size. These are similar on both ventral and dorsal surfaces. There- 

 are about ten primaries in each vertical row, and a like number of sutural pits. The 

 sutural pits of the ambulacral segments, and of the interambulacral avenue-margins, are 

 shallower, smaller, and the former more numerous. They are all distinctly defined, and 

 not confluent. Each ambulacra! plate bears on its outer half a primary tubercle nearlv 

 equal to that on an interambulacral plate, and similarly surrounded by secondary tubercles 

 and granules. There are about fifteen of the ambulacral primaries in each vertical row. 

 The pairs of pores in the avenues are very obscurely three-ranked, and similar in 



