‘PORCUPINE’ DEEP-SEA DREDGING-EXPEDITIONS. 
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sions of the tooth-sockets bear short epiphyses ; but these are not united into an arch, as 
in the Ecliinidce. The teeth are powerful, but they are simply grooved without a median 
longitudinal ridge. The primary spines are remarkably large, sometimes three times the 
diameter of the test in length : they are cylindrical, or prismatic, or tapering, or .flat- 
tened, or club-shaped ; smooth or finely striated, or ornamented with longitudinal spiny 
ridges, or regularly or irregularly tuberculated. The secondary and smaller spines are 
flattened and striated. The pedicel larige differ in form in different genera. 
Thus defined, the Cidaridae form a very natural group. 
They are at once distinguished from all the other families of the “ regular ” Urchins, 
with the exception of the Saleniadae, by the extreme narrowness of the ambulacra. They 
resemble the Saleniadae in general appearance, but they differ from them in the structure 
of the peristome and in that of the apical disk, which, in the Saleniadae, includes a large 
plate in addition to the normal double range of five “ ocular ” and five ovarial plates. 
They approach the Echinothuridae in the important character of the continuity of the 
rows of ambulacral tube feet through imbricated scales over the buccal membrane and 
up to the edge of the mouth, in the condition of the epiphyses of the tooth-sockets, and 
in the form and structure of the teeth ; but they differ from them widely in the homo- 
geneity of the tube feet, in the remarkably solid inflexible nature of the test, and in the 
form of the spines and pedicellariae. 
They resemble the Diadematidae in the structure of the tooth-sockets and teeth, but 
they differ from them in the continuation of the ambulacral over the buccal membrane, 
in the absence of notches in the peristomial rim, which in the Diadematidae are par- 
ticularly deep, and in the structure of the spines and pedicellariae. 
From the Echinidae they are distinguished by the absence of the calcareous arches 
uniting the halves of the tooth-sockets, by the absence of the median ridge in the con- 
cavity of the teeth, and by the absence of notches in the peristome and of branchiae. 
Genus Cidaris, Klein. 
Test globular, slightly and equally flattened at the oral and apical poles. Ambulacral 
areae very narrow, bearing miliary tubercles only, in from four to six rows. Pore-areae 
simple : the pores of each pair are contiguous, or, when slightly separated, they are 
united by a groove. The interambulacral plates are seven to ten in a row ; the areolae 
are large, circular, or transversely elliptical ; the bosses supporting the primary tubercles 
are crenulated or smooth. The ovarial plates are large, more or less rectangular or 
shield-shaped, with a large defined perforation for the duct of the ovary passing through 
the plate about one third of its width from the outer margin. The primary spines are 
large and variously formed in different species. The pedicellariae are variously formed, 
but they are all 3-valved. The ovaries are compact and lobed, and their outer wall is 
supported by irregularly shaped fenestrated calcareous plates. Fenestrated plates like- 
wise occur in the walls of the intestine. 
Hitherto the attempts to subdivide the family of the Cidaridae into genera has not 
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