THE MOUNT DESERT REGION O 



Order ECHINODERA 



Suborder HOMALOEHAGAE 



Pycnophyidae 



Pycnophyes Zelinka 



Pijcuophyes frequens spec. nov. (figs. 1 to 3) 



The nearest relative of this species is P. communis Zelinka, 

 to which it runs out in his key (Zelinka, '28, pp. 309-310). 

 It has the same parallel sides to the body. The length- 

 breadth ratio is 4.3^.6 : 1. 



Length : 0.73 to 0.81 mm. ; breadth, 0.16 to 0.19 mm. 



Middorsal spines are present, though very short; the first 

 three and the last three are pointed, the others are rounded. 

 The last spine is exceedingly short and does not always seem 

 to be present. 



The dorsal pachy cycle (Pachyzyklus of Zelinka) of zonite 

 III has no cusps at the posterior margin. The median arc 

 is more than one-third the width of the zonite. The ventral 

 pachycycle of zonite IV appears rather broader than in 

 P. commimis. 



The posterior extremity of the male has the nearly straight 

 median portion, bounded by a spine at each end and provided 

 with short fine hairs, which is found in P. commimis. In the 

 female the delicate membrane between the bounding spines 

 is nearly semicircular and supported by a few, fine, 

 unbranched processes. 



Nearly the whole of each dorsal plate and an oval patch 

 just lateral to the middle of each ventral half-plate is per- 

 forated by very small pores, which give the areas a finely 

 stippled appearance. 



Habitat: Fine, sticky, brown mud in 40 to 120 feet of 

 water, probably also in deeper water. It is quite common. 



Type: G2 (Collection Biological Survey Mount Desert 

 Region). 



Remarks : This species may be readily distinguished from 

 P. communis by the greater size and by the lack of cusps on 

 the posterior margin of the dorsal pachycycle of zonite III. 



