.•?(;s TACxK SKOGSBERG 



2) Of the six species of this genus known from colder seas (Arctic and Antarctic) four* 

 are characterized by having these bristles broken off in older females. 



These facts indicate that external, climatic factors have perhaps caused this peculiar 

 convergence.** 



It does not seem impossible that in the case of species which are characterized by having 

 the natatory bristles of the second antenna unbroken throughout the whole life the females 

 are impregnated several times. The statement made by Gr. W. MtJLLER, 1894, p. 174, according 

 to which Fh. (Ph.) interpuncta lays at least two lots of eggs, seems to me to support this. 



Genus Philomedes W. Lilljeborg. 



Cyprid/ina (part.) autorum; e. g. W. Baiud, 18.5U a and ¥n. MULLER, 1870. 

 Asterope, S. FischePv, 185.5. Philomedes (= S) + Cypridina (= ? and juv.), \V. Lh.l.uokorg, 

 1853. Philomedes {= S) + Bradycinetus (= ? and juv.), (i. (). Rars, 1865; (J. S. Brady, 

 1868b and 1871. Philomedes (= <S, ? and juv.) autorum; e. g. CI. 0. Sars, 1869 

 and 1887; G. W. Muller, 1894; G. S. BRADY and A. M. NORMAX, 1896. Philomedes (part.). 

 G. W. MiiLLER, 1912. 



^^'ith regard to the relation t)f Pleoschisma and Tetragonodon to this genus cf. above 

 the remark below the sub-family. 



Diagnosis: — Cf. G. 0. Sars, 1887, p. 45 and G. S. BRADY and A. M. NoRMAN, 1896, ji. (i5.'}. 



Description: — .Shell: — This has marked sexual dimorphism. 



Female: — The s li a p e of the shell varies rather considerably. The rostral incisur 

 is of a somewhat varying type, but is most frequently deep and narrow. The sculpture of the 

 surface seems in most cases to be very weakly or even not at all developed ; in some cases, 

 on the other hand, it is very powerful. Seen from inside: The part of the shell between 

 the list and the posterior margin of the shell is flattened and not curved in like a siphon, so that 

 the two valves are near each other at this part when the shell is closed; only in exceptional cases 

 is there any indication of a siphon: (cf. the description of Ph. ( Scleroconcha) Appellofi). 

 Medial bristles: These had in the species investigated by me almost exactly the same type: 

 (_)n the rostrum there was a row running at some distance from and almost parallel to the ventral 

 part of the anterior margin of the rostrum sometimes continuing a little way along the anterior 

 margin of the rostral incisur. Most of these bristles were rather long and finely feathered; 



* U Jiiay l)i: poirilcd out Ihal /'//. (I'll.) nrhiriili:ris. a species from the Viilarelie, (Irsci-ilicd U\ (',. S. l!it,vriY, 



whii'h is certainly very i.losely rclalcil lo Ph. (J'li.) niliinda, has. according; to Ihis author's drawing, 1007, pi. I, fi^. 8. 



liiiiM unbrolvCM natatory Ijristles on tlie second antenna; tliere is, however, no inl'ormalioii as to whether the female from 



wliich llio antenna that is roproHueed was taken had efjsi'sin the brood chamber or if it was still in the jilankton stage. 



«'• ><ei' I;, llrssr, ami I'. Unii.riN'. ..■j'iriliaii nn.l 'I'i. ilrlirn-. I'.U'i, II. |i. .s;r,. 



