412 PEOCEEDINGS OF UNITED STATES NATIONAL MUSEUM, 



beeu i^oiiited out, the single large dentate laterals of Pectinodonta may 

 represent, in the other division of the order, each a consolidation of the 

 three typical laterals of Acmcva. 



The name Onychoglossa has been used by G. O. Sars.(1878) to denominate 

 the same group and as indicative of the same characters as those pos- 

 sessed by the Docoglosm (Troschel, ISGl), as revised by me eight years 

 previously. I do not see any especial gain which might result to science 

 from substitutiug tlie newer for the older name. 



The relations of the groups may be expressed somewhat as follows : 



Order DOCOGLOSSA. 



Shell wholly external, di^h shaped, with ax)ex anteriorly directed; 

 animal with two short tentacles, a iion -extensible muzzle; branchife 

 external or none; renal and anal ai)ertures situated above the neck, 

 between body and mantle edge; no coj)ulatoiy or external genital 

 organs ; mouth provided with a horny jaw and long radula with pecu- 

 liar teeth; dental formula not exceeding., .>ovq' i^ietamorpbosis of 

 the embryo taking place in the egg, which is fertilized in the ovary. 



Sub6rder ABRANCIIIATA. 



Animal without external brancliiie. Embryonic shell spiral. 



Family LEPETIl)^. 



Subfamily Lepetinw. Without eyes; with a marginated muzzle ex- 

 tended into (on each side) a tentacular x)rocess. Uncini erect. Dental 



formula _^^(?=, -3 »3j-,). 



T . f^ r Lepeta s. s. (4- Pilidhim Forbes uou Middendorf). 

 Lepeta Gray. ,, ^ \ ' ^r. , , , ,. 

 ( Crxjptobranchia Middendori. 



Subfamily LcpctellincG. With eyes; other soft parts as in Lepeta, 



Uncinus scale-like. Dental formula .^ - ( ? = ., ,., om )• 



1 (L'L) 1 \ 1 (o + o) ly 



Lepetella Yerrill. 



Suborder PROTEOBRANCHIATA. 



Animal with external branchiae. Embryonic shell conical. 



Family ACM^EID^. 



With a plumose cervical branchia ; with or without a branchial cordon j 

 muzzle frilled ; no rhachidian tooth. 



