132 



DR. T. DAVIDSOX OX EECENT BEACHIOPODA. 



Fiff. 10. 



incomplete foramen, marp^ined anteriorly by the umbo of tlie opposite valve, and laterally 

 by two small deltidial plates ; beak-ridges sharply defined, leaving between them and 

 the hinge-line a small triangular flattened space. Surface of valves smooth, or Avitli from 

 two to six rounded ribs, more or less defined in different specimens. Sliell semitrans- 

 parent, white or yellowish brown. Shell-structure punctate. 

 Length 2^ lines, breadth 2 lines, depth 1 line. In the inte- 

 rior of the dorsal valve the hinge-plate is long and narrow, 

 without any defined cardinal process. Under its centre a 

 triangular-shaped j)late or septum gradually rises, and extends 

 to four fifths of the length of the valve, being most 

 elevated near to its anterior extremity. Loop two-lobed, 

 attached to the base of the hinge-plate and again to the 

 anterior extremity of the submarginal sejjtum, and more or 

 less confluent with the valve. Labial processes folded into 

 two lol)es, united by a membrane forming a brachial disk 

 fringed with long cilia. Mantle extending to the margin, 

 closely adherent. In the interior of the ventral valve a small 

 septum extends from under the beak to about half the 

 length of the shell ; margins of the valves much thickened 

 within. 



Bah. Mediterranean, at depths of from CO to 100 fathoms ; 

 Bay of Naples, off the islauds of Capri and Ponza ; J^gean 

 Sea. 



Obs. Some malacologists have expressed the opinion that 



Terehratula semhiula, Philippi, is a synonym of C. neapoli- 



tana ; but the foraminal umbo of the dorsal valve in the 

 first-named shell would render that view doubtful. 



Exteriorly Cistella neapoUtana is a well-marked species, 



although it varies a good deal in shape, being also either 



quite smooth or obscurely ribbed. 



Kowalevsky has described and illustrated in great detail 



the development of C. neapoUtana. MM. Oehlert and Deniker 



have published an excellent summary of this memoir, most 



useful to those who are unable to read the Russian language. 



Kowalevsky states that the eggs, after they are detached 



from the ovary, fall into the general cavity of the body, 



enter the oviducts by the funnel-shaped opening of these 



organs, and pass into the incubatory pouches, situated on the 



ventral lobe of the female individual, where they are deve- 

 loped. He is of opinion that fecundation must, without 



doubt, be accomplished either during the passage of the egg 



along the oviduct or in the general cavity. 



Argiope neapoUtana (after 

 Kowalevsky). 



A. Egg after the invagination of 

 a part of the blastoderm : 

 d, cavity formed by the in- 

 vagination ; a, orifice of the 

 cavity ; o, exterior layer (up- 

 per) ; V, interior layer. 



E. The embryo divided into two 

 segments. 



C. Embryo, in which the folding 

 of the mantle already covers 

 a part of the caudal seg- 

 ment : rt, cephalic segment; 

 6, thoracic segment ; c, cau- 

 dal segment ; s, bundles of 

 bristles. 



