ZOOLOGY. G09 



or ouly with feeble indications of tb-em in tbe binge; two equal muscu- 

 lar impressions; pallial line entire. Palaeozoic. 



"Orel. 2. Desmodonata. Teetb of tbe binge none or irregular, con- 

 nected witb tbe ligamental processes ; two equal muscular im])ressions; 

 piillial line sinuated. FhoIadoinykUc, CorbuUdw, Myida\ Anatinidce, 

 Macfridw, Fapliiidce, Gli/cymerid(v, {f) Solenidw, and all Tuhicola. 



"Urd.3. Taxodonta. Teetb of tbe binge numerous, not differen- 

 tiated, in a straight, arcuated or angular row ; two equal muscular im- 

 pressions. Arcidci'. Niiculidcc. 



"Ord.4. Hetekodonta. Teetb of tbe binge few, distinctly separated 

 as cardinal and lateral, alternating, exactly tilling tbe pits of the op- 

 posite valve; two equal muscular impressions. Unionidce, CardinUdw, 

 Astartidce, Craf^satelUdcc, Megalodontidw, Chamidce, Tridacnidcc, Erijci- 

 nidcc, Lucinidw, Cardiidce, Cyrenidce^ Gyprinidce, Veneridcv, Gnathodon- 

 tidcc, Tellinidcc, Donacidie. Tbe Trigoniidw will form a distinct sub- 

 order. 



"Ord. 5. Anisomyaria, or Dysodonta. Teetb of tbe binge none or 

 irreguhir; two very inequal or only one muscular impression ; pallial 

 line entire. 



(«) Heteromyaria : AvicuUdce, 3Iytilidw, Prasitiidce, Pinnldic. 



(h) Monomyaria : Pectinidce, Spondylidcv, Anomiidce, Ostreidcc.^^ 



{Zoological Record, 1883, pp. 86 and 87, Moll.) 



^r. von Martens, certainly a most competent judge, bas expressed 

 ibe opinion tbat tbis classification "bas several advantages in com- 

 parison witb bitberto accepted classifications: (1) tbe distinction of a 

 limited number of natural types, instead of an artificial separation into 

 Monomyaria and Dimyaria, or Asipbonida and Siphonida ; (2) the union 

 of tbe Heteromyaria and tbe Monomyaria into one common chief di- 

 vision;" and (3) "tbe constitution of a special chief division for the 

 Arcidfe and Xuculidae, as these families offer very peculiar characters 

 as well in tbe shells as in tbe gills and foot." 



Tbe present recorder is unable to appreciate anj- superiority of the 

 new arrangement over tbat based on the muscles, and there are cer- 

 tainly more exceptions of the contents of the so-called "orders" to their 

 diagnoses than in the case of tbe groups defined bj^ tbe muscles. As 

 Dr. Paul Fischer bas already remarked (Journ. Conch,, v. 24, p. 121), a 

 single family (tbe Unionidse) has representatives not only deviating 

 from the diagnosis of tbe including "order" (Heterodonta), but exhibit- 

 ing characters assigned to two others, Anodonta recalling tbe Palaeo- 

 concha^ or Cryptodonta, and Pleiodon tbe Taxodonta. Undoubtedly 

 Dr. Neumayr knew of these exceptions and regarded the forms and 

 questions as derivatives from tbe normal Heterodonta. But the dif- 

 ferences from the type and assumption of characteristics of others 

 nevertheless exist. For tbis, if for no other reason, the value of such 

 characters for orders is nullified. There is also a want of co-ordination 

 between tbe binge structure and modifications of other parts which 

 S. Mis. 33 39 



