554 



ECHINODERMATA ECHINOIDEA 



Fam. 2. Nucleolidae. "Petals" distinct; peristome as in 

 the foregoing family. No floscelle. Nucleolites, with the anus 

 in a furrow. Anochanus, with a concave apical system serving 

 as brood-pouch. 



Fam. 3. Cassidulidae. " Petals " usually distinct ; peristome 

 eccentric, but provided with a well-marked floscelle. 



Uchinolampas, with the anus on the under surface. 



Neolampas, with the anus on a projecting papilla. One 

 specimen of this genus has been dredged in the British area. 



The three foregoing families probably use their tube-feet to 

 walk with, and bury themselves only to a slight extent. They 

 are often united as a sub-order, the Asternata, and distinguished 

 from all the rest which possess an eccentric mouth and well- 

 marked plastron. These families are then grouped together as 

 Sternata. They are as follows : 



Fam. 4. Ananchytidae. 1 Spatangoidea with elongated apical 

 system, ambulacra all similar and not grooved. Petals feebly 



Fig. 249. Pourtalesia jeffreysi, slightly enlarged. (From Wyville Thomson.) 



marked. Pourtalesia, with bottle-shaped posterior prolongation 

 of the test. Platyhrissus, with flattened est. 



Fam. 5. Palaeostomatidae. An aberrant family consisting 

 of one genus, Palaeostoma. Petals grooved, with a peripetalous 

 fasciole, but peristome central and pentagonal. 



Fam. 6. Spatangidae. Spatangoidea of more or less flattened 

 shape, with well-marked petals and a sub-anal plastron as well as 



1 This family includes three families discriminated by Meissner (Bronn's 

 Thier-Beich, vol. ii. Abt. 3, Buch iv. "Die Seeigel," 1904, p. 402), viz. : Ananchy- 

 tidae, Pourtalesiidae, and Urechinidae. They only differ in the pores for the 

 tube-feet, which are paired in the first, slit-like and single in the second, and 

 single in the third. 



