The I'eii'is-hone, or " Baculum^^^ in certain Sipiirreh. .'i83 



LlTI-.K.VTL'RIC CITKO. 



[i] ANi»ni:ws, C. W. ' A M<.noprnph of Chrisdiina Islftiid.' Published 



by tlie IJritish .Miisfuin, liKJU. [N<jte on Cardisoma caruijix 



(C. hirfijh'f), p. lt)4.j 

 [i] Bayi-is, II. A. "Olijrocliicta" : British Antarctic ('Terra Novn ') 



Kxp. I'.ilO. Zooloyy, vol. ii. no. 1*, pp. l.*5-l8. Published by the 



Ikiti-sh Muauuui, llU.j. 



Otiikij Pai'kks consulted. 



[3] Richard, J. " Essai sur les Parasites et les Coramensaux des Crus- 



tact5s." Arch. Parasitol. toui. ii. pp. .')4S-f>'X^. Paris, 1899. 

 [4] WiLso.N, C. H. "Crustacean Parasites of West Indian Fi.shes and 



Land Crabs." Proc. U.S. Nat. Mus. vol. xliv. (WHS) pp. 189-277. 



[Omcn'nrula, R new (Tenus of Copepoda, Parasitic iu Cardisoma 



ijuaiifiumi, gills, p. 2(54.] 



XXXIV. — The Penis-hone, or '"'■ Bacuhim,^^ as a Guide to 

 the Classijication of certain Squirrels. By OldfielD 

 Thomas. 



(Published by permission of the Trustees of the British Museum.) 



There lias always appeared to be sometliing wrong with the 

 inclusion ot" tlie (h-iental squirrels in the ."ame genus as 

 t'cinrus vulgaris, although when classifying the group some 

 yeais ago I was unable to find any material ditterences in 

 their skulls and teeth. 



Now, however, I have Ibund a character by which such 

 squirrels as are still put in Saurzis may be sorted into 

 several group?, each sharply defined from the others. 



This is in the structure ot" the os penis, which show.s very 

 striking ditl'erences between the various groups of species, 

 and may evidently be of great service in classifying the 

 members of tins difficult family. For many years 1 iiave 



of this species. The specimens difTer in the form of the carapace and 

 third niaxillipeds from G. malpileyisis as described by Faxon (Mem. Mu.". 

 Conip. Zool. xviii. 189^, p. 28J; in the proportions of the carapace and 

 legs from G.diyueti, Bouvier, as rede.scribed by IJiithbiin (U.S. Dep. 

 Ag-ric. N. Amor. Fauna, no. 14, 1899, p. 73) ; and in Iiavin-,' .".ix spine- 

 rows on the dactyli, from G. lateralis (Freminville). I am not aware 

 that anyone has attempted a detailed criticism of Ortmann'a opinion 

 (Zool. Jiihrb. Abth. f. Syst. x. 1897, p. 3;i7) that all the American forms 

 belonging to this genus can be referred to a single species, G. ruricola 

 ( Linn.).'' 



