PYCNOLAMPAS OVIFORMIS. 155 



is more distinct in the larger than in the smaller specimens, and in ambulacrum 

 III being perfectly flush with the surface of the test instead of being sunken. 

 There are a few big primary tubercles in the interambulacra within the peri- 

 petalous fasciole, as in Homolampas, but the scrobicules are not sunken as in 

 that genus. This difference, however, is very likely a matter of age and I believe 

 that in the adult Pycnolampas the scrobicules will be found to be sunken. Until 

 adult specimens are found, however, the original diagnosis of the genus stands. 



Pycnolampas oviformis. 



A. Agassiz and Clark, 1907. Bull. M. C. Z., 60, p. 253. 



Plate 147, figs. 4-6. 



Length 22 mm.; breadth where widest, just back of abactinal system, 17 

 mm.; height where highest, just back of abactinal system 9.5 mm. The area 

 enclosed by the peripetalous fasciole is about 14 mm. long by 12 mm. wide. 

 The fasciole itself is very narrow, well marked on the sides but not so distinct 

 anteriorly and posteriorly. Ambulacrum III is indistinct, not at all depressed 

 and with few minute pores. Poriferous areas of the other ambulacra evident 

 (PI. 147, fig. 5), those of the posterior pair especially tending to become petaloid 

 within the fasciole. Periproct about as wide as high, occupying most of the 

 vertical posterior end of test. Subanal fasciole well marked, its enclosed area 

 about 5 mm. wide and 4 mm. long. Peristome almost perfectly flush with oral 

 surface of test, with no distinct labium and with mouth near its center; the 

 peristome is 3.5 mm. wide, 3 mm. long and its anterior margin is only 5 mm. 

 from the anterior margin of the test. The labrum (PL 147, fig. 6) is very long 

 and narrow, in contact with three ambulacral plates on each side. The pos- 

 terior pair of ambulacra, orally (PL 147, fig. 6) are broad and perfectly bare; 

 five ambulacral plates enter the subanal fasciole on each side but only three carry 

 large penicillate feet (PL 147, fig. 4)- The color of the preserved material is 

 very pale yellowish or grayish, with the fascioles darker. 



The primary spines are 6-8 mm. long and appear under a lens to be perfectly 

 smooth. Secondary spines similar but much smaller, about 2 mm. long, are 

 common especially near the ambitus, and miliary spines, a millimeter or less 

 in length sparsely cover the test, except orally in the ambulacra. Pedicellariae 

 of three kinds occur but they are not at all distinctive. The tridentate are 

 rather rare; they have very narrow nearly straight valves, about half a milli- 



