CO^CnYUA—DITHYRA. xM. 



2. subauriculata, depressa, striis rectis nniformihus. 

 flattish, with straight uniform strise. 



48. AVICULA. 



1. Hirundo, caudd longitudine ala. 



the tail as long as the wing. 



49. Pinna. 



i . ingens, arcuathn striata, postich truncata recta. 



with curved striae, truncate and straight at the 

 hinder side. 



2. fragilis, arcuatim striata, postich producta rotundata. 



with curved striae, produced and rounded at the 

 hinder side. 



3. pectinata, costis 16 confertis sqttamosis. 



with 16 close-set scaly ribs. 



4. papyracea, costis 9 remotis muticis. 



with 9 remote unarmed ribs. 



5. muricata, carnea, costis 7 concavo-spinosis. 



pale red. with 7 ribs armed with concave spines 



50. Anomia. 



1. electrica, jwUucida succinea, 



transparent and amber-colored. 



2. Ephippium, suborhicularis, margine undato, 



somewhat orbicular, undulate at the margin. 



3. Cepa, ohovata planiitscula, intus rosea. 



oboval flattish, rosy on the inside. 



4. Squamula, suLoihicularis Itevis pellucida. 



somewhat orbicular smooth and transparent 



