NO. 19.] ECHINODERMS OF CONNECTICUT. 113 



The mouth is situated a little anterior to the center of the 

 oral surface, while the posterior opening of the intestine lies 

 between the central end of the interradial lunule and the mouth. 



In some specimens one or more of the lunules, as shown on 

 Plate XXVIII, may extend quite to the margin of the disk. 

 Such an abnormality may be caused either by accidental injury 

 or by the failure of the two edges of the lunule to unite together 

 distally in the young urchin. 



This species occurs locally from Nantucket to Brazil in shal- 

 low water, although it is not common north of Cape Hatteras. 

 In Long Island Sound the species has been collected at Hunting- 

 ton, Long Island, a number of specimens from this locality 

 belonging to the Yale University Museum. 



A description of the digestive system of this species may be 

 found on page 95, while Plate XXIV, fig. I, illustrates the 

 internal anatomy. 



In a paper by Grave* the structure and development of the 

 larvae have been described and illustrated. 



* Johns Hopkins Unit-. Circular, No. 157, 1902. 



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