JUKES-BROWNE : ON SOME GENEKA OF VENERID^. 241 



of his groups, and though in his tabular view he gives in most cases 

 single examples, under Katelysia he gives two species, V. scalarina, 

 Lam., and V. exalhida, Chem., so that it is clear that he meant them 

 all to be taken as examples, not types. 



In his later revision of the family ^ he gives a full definition of the 

 group characters in Latin, the part referring to the teeth reading thus : 

 " dentes cardinales valde divergentes, triangulares, obliqui, in valva 

 sinistra dens medianus crassus, bisulcatus, in dextra secundus tertiusque 

 fissi." Moreover, he therein regards Katelysia as a ' subgenus ' and 

 divides it into three sections, each of which is briefly defined ; these 

 sections include the following species : — 



§ 1. ^. scalarina, Lam. ; II. aphrodina, Lam. ; IT. regular is, Desh. 



§ 2. K. exalhida, Chem. ; K. lenticular is, Sow. ; JT. quadrangularis, 

 Ads. & E.ve. ; K, tenuilamellata, Sow. 



§ 3. K. astartoides, Eeck ; K. Creplini, Dunker ; K. telliniformis, 

 Phil. 



Romer, therefore, did not indicate a type either in 1857 or in 1864, 

 and in this case Dr. Dall does not suppose that he did, but he says that 

 "the first to accept the name was Tryon in 1884, who selected 

 V. scalarina, Lam., as type of Romer's group, in which he was 

 followed by Fischer, who changed the name to Catelysia^ 



"Whether Tryon can be said to have selected V. scalarina as the type 

 or not, it is the species which should be so regarded ; and as Dr. Dall 

 accepted it in 1903, I definitely adopt it as the type of a restricted 

 Katelysia group, corresponding to the first section of Romer's Katelysia 

 of 1864. 



It will be noticed that the second section of Romer's Katelysia is 

 what may be called the exalhida group, for everyone admits that the 

 three species exalhida, lentieularis, and quadrangular is are closely allied. 

 V. tenuilamellata, however, must be excluded, as it was based on a shell 

 which is probably a young specimen of V. Campechiensis, Gmelin. 



When Dr. Dall in 1902 created a genus Marcia, with V. exalhida 

 as type, he made Katelysia a subgenus of it, and placed the species 

 quadrangular is and lentieularis under the latter as a separate section 

 with the new name of Samarangia.' His reason for separating these 

 species from exalhida seems to have been that he imagined the latter 

 to have four cardinal teeth in the right valve, Avhile he credited the 

 others with the normal number of three. 



I have only been able to examine one specimen of V. exalhida, which 

 was kindly lent to me by Mr. J. J. MacAndrew, and in this there is 

 nothing but a slight ridge at the base of the nymph, just as there is in 

 V. lentieularis and in many other shells, such as Gomphina donacina 

 and in several species of Chione, especially Ch. Gnidia and Ch. amathusia. 

 Dr. Dall himself observes that "in a few of the larger species [of 

 Chione~\ a feeble fourth cardinal is sometimes present below the 

 ligament," but he does not for that reason propose to separate these 

 species as a distinct section of Chione ; why, therefore, should V. exalhida 



1 Malak. Blatt., 1864, p. 169. 



2 Proc. U.S. Nat. Mus., 1902, vol. xxvi, p. 361. 



VOL. VIII. — APRIL, 1909. 19 



