H2 CONNECTICUT GEOL. AND NAT. HIST;. SURVEY. [BuU. 



Mellita pentapora (Gmelin) 



Key-hole Urchin 



Plate XXIV, fig. I ; Plate XXVIII. 



The name Mellita testudinata was given to this species by 

 Klein in 1734; but, as this long preceded the Linnsean code, the 

 specific name pentapora proposed by Gmelin in 1788 should be 

 adopted. Many authorities, however, insist upon the use of 

 testudinata.* 



This species has a flat test, and in this respect bears a super- 

 ficial resemblance to the common sand-dollar, but is easily dis- 

 tinguished by the five narrow openings, termed lunules, which 

 pass completely through the body as shown on Plate XXVIII. 

 One of these lunules is situated in the posterior interradius, about 

 half-way from center to circumference, while the other four are 

 symmetrically placed, one in the center of each radius except the 

 anterior. 



The flattened test is densely covered with short but slender 

 spines of a brownish color. The general color of the living 

 animal is commonly pale brown, .sometimes with a tinge of green. 



Especially after the spines are removed, the petaloid ambu- 

 lacral areas are conspicuous on the aboral surface. On the oral 

 surface the narrow ambulacral furrows are provided with paired 

 branches which extend peripherally from the mouth to the edge 

 of the disk. Each of the main branches has lateral offshoots 

 (Plate XXVIII). 



* In a recent paper {Annals and Mag. Nat. Hist., 8 ser., toI. vii, 1911) Qark recom- 

 ■ends the adoption of the name quinquiesperforata Leske for this species. 



Explanation of Plate XXVIII. Key-hole Urchin, Mellita pentapora. 



(Natural size.) 

 Aboral and oral surfaces of two dried specimens. The minute spines 

 have been removed from the left-hand side of each. The aboral surface 

 shows three of the five ambulacral areas, " petals "- The mouth lies in 

 the center of the oral surface, with the anus near the inner end of the 

 median lunule. One of the posterior lunules in the lower figure is ab- 

 normal in that it remains open to the edge of the disk. 



