SCUTELLIDAE. 05 



determined to name it as a new species of Echinocyamiis. It is obviously differ- 

 ent from the two other Hawaiian species collected by the Albatross, but how 

 much of this difference is due to individual diversity, I cannot decide. It is 

 hartl to beheve, however, that an individual variant of either elongatus or scaber 

 would show the characters of this specimen. 



Echinocyamus macrostomus. 



Mortensen, i'.iOT. Ingolp Ech., pt. 2, p. 30. 



Tliis Atlantic species is notable for its living at great depths. It is known 

 only from stations in 800-1,270 fathoms. 



SCUTELLIDAE Agassiz. 



The form of the test and the condition of the auricles in the various members 

 of this family indicate that it is a highly specialized group and this opinion is 

 confirmed by the pedicellariae, which are rarely abundant, but are often very 

 few in number and usually have only two valves. Nothing is known of the 

 pedicellariae of Rotula and I regret to say no specimens of the genus, except 

 bare tests, are in the M. C. Z. collection. Judging from the characters of the 

 test alone, Rotula may well be considered the most higUy specialized form of 

 clypeastroid known either living or fossil. On the other hand, all the characters 

 of Echinarachnius point to it as one of the least specialized members of the 

 family and it is very possibly quite near the ancestral stock from which the scu- 

 tellids arose. The recent genera of the family are easily distinguished from 

 each other by very obvious external characters, the presence or absence of 

 lunules and marginal slits being the most important. When lunules are present, 

 their position and number furnish good, constant characters, but the size is 

 often very variable, especially in Encope. The latter genus is further remarkable 

 for being the only genus in the family which has retained five genital pores. 

 The position of the periproct and of the apical system may be useful characters, 

 and for specific differences the lengths of the different petals in relation to each 

 other is often very important. The following key will serve to distinguish seven 

 genera of recent scutellids. 



Key to the Genera of Scutellidae. 



Test without marginal slits or lunules. 



Abactinalsystemat apex of test; petals about equal; periproct marginal . . . Echinarachnius. 

 Abactinal system posterior to apex; posterior petals much shorter than others; 



periproct on oral surface uendrasler. 



