GONIOCIDARLS CLYPEATA. 27 



larger in young specimens than in other Goniocidaridae. In a specimen 13 

 mm. in diameter there are seven and seven plates; in a specimen of 18 mm. 

 there are only seven and eight plates. In a specimen only 8 mm. in diameter 

 there are already five and five plates. With the exception of the variation 

 in the radioles and the absence of the cup-bearing radioles, there are but 

 slight differences to be noted in the structure of the test, the sunken median 

 ambulacral and interambulacral areas, the shape of the abactinal system and 

 of the anal system, between the smaller and larger specimens examined. 

 The smaller specimens usually carry only the serrated radioles. Usually a 

 specimen 12 mm. in diameter carries a few disk-bearing radioles ; though in 

 the largest specimens collected all the radioles, actinal as well as abactinal, 

 belong to the serrated type. 



The series of specimens before us leaves little doubt that Doderlein's 

 Porocidaris gracilis ^ was based on a young specimen of this species, in which 

 the expanded radioles were not developed. 



There are only two kinds of pedicellarioe present in clypeata, as the 

 tridentate seem to be wholly wanting. 



The large globiferous pedicellariae (PI. 10, figs. 27-29) show considerable 

 diversity in the shape of the valves; normally (PL 10, fig. 29) they are like 

 those of G. hiscrialis but sometimes they are much longer and narrower, with 

 a large terminal opening (PI. 10, fig. 28) or still narrower, slightly curved 

 and with an end-tooth (PI. 10, fig. 27). They measure from .50 to .90 mm. 

 with the stalk somewhat shorter. These pedicellariae are somewhat rare 

 and occur only on the interambulacra. 



The small globiferous pedicellariae have a strong end-tooth on the valves ; 

 sometimes (PI. 10, fig. 30) they are like those of G. mikado, while others 

 (PI. 10, fig. 31) are like those of biserialis. The valves are .25-.50 mm. in 

 length, while the stalks are shorter, longer, or twice as long. They are 

 abundant everywhere. 



Station 3748. Off Suno Saki, Sagami Bay, Japan. 73-200 fathoms. 

 Yl. s. rot. CO. 



Station 3749. Off Suno Saki, Sagami Bay, Japan. 83-158 fathoms. 

 Bl. s. sh. 



Station 3751. Off Suno Saki, Sagami Bay, Japan. 140-148 fathoms. 

 Gn. m. vol. s. 



^ Dorocidaris (?) gracilis, 1885. Arch. f. Naturg. 51 Jahrg. Bd. 1, p. 78. 

 Porocidaris gracilis, 1887. Jap. Seeigel, p. 8. Pis. IV, figs. 8-20; VIII, fig. 5. 



