OF WESTERN SIND. 15 



orifice being just apparent when the test is viewed from above. In some specimens 

 the median interradial portion of the odd interambulacrum is rather bombous and 

 subcarinate in the neighbourhood of the orifice ; but this is a character subject to 

 more or less variation, as is also the development of the subanal groove : these modi- 

 fications will be mentioned below. 



Variations. The variations of form, in specimens of the same size, chiefly affect 

 the general shape. Some are more circular, more swollen posteriorly, and broader than 

 others. Indeed there almost appear to be two types of this species, one of greater length 

 than the other in relation to breadth and with a more angularly pentagonal peristome ; 

 but intermediate forms unite them in one species. In some examples, again, the inter- 

 radial areas are more bombous around the peristome, which is less transversely elongate 

 and rather more deeply sunken, the bourrelets being narrower and less prominent, and 

 the phyllodes slightly sunken, which brings out the latter into very distinct definition. 



Premature Forms. A large series of specimens was collected, so that it is possible 

 to trace the method of growth and the changes which occurred in the morphology of 

 the test in young and older forms. 



Young specimens, -^q inch in length, are of the same breadth, and measure rather 

 more than xo i^^ch in height. The mouth is very slightly excentric ; the periproct 

 large, and not in a groove, but on the rounded margin, close on to the dorsal area, and 

 consequently at a very much higher plane than the mouth. The globular appearance 

 is marked. 



Another, rather more than -^ inch in length, is rather less in breadth, and is 

 j%- inch in height ; it has the mouth more excentric ; the keel on the back has com- 

 menced; and the periproct is at its end and high up, there being no groove. The 

 ornamentation is very similar everywhere. 



Another, not quite ^ inch broad, is rather over -^ inch in length, and the height 

 is rather over -^ inch. ^^, -^g, and -^ are the respective measurements of another 

 specimen. 



Hence it follows that Echinanthus pumilus is more globular when young, 

 and that during the process of growth the test increases more in length than in 

 breadth, and that there is a still greater proportional diminution in height. In 

 addition to the greater breadth of the young forms when compared with the older, the 

 test is relatively higher behind, and the apical system is slightly more excentric than 

 the peristome. The character of the ambulacra appears to undergo little change, even 

 the wavy irregularity of the zones of the odd anterior petal being present in the early 

 stages. The conjugation of the pores, however, is not apparent in very young phases. 



Remarks. Fractured specimens show a thin test, and that there is not the 

 slightest arrangement of internal pillars or doubling of the walls. The character of 

 the present species recalls strikingly that of small specimens of the Echinanthus 

 scutella of European geologists ; and the conformity of the structure of the mouth of 

 the Sind form to that of known Cassidulidse is absolute, and is altogether distinct from 

 that of the so-called Echinanthi of A. Agassiz, which are true Clypeastroids. 



The present species is well characterized, and readily distinguishable from other 



