12-4 PROCEEDINGS OF THE ACADEMY OF [1888. 



The shells of Maelia are small for the body, and the siphons are 

 so large that they cannot in any way be drawn into the shell, a large 

 portion of the mantle also is without the limits of the shell, so that 

 the edges of the shell do not even touch in life. 



In Teredo, no hinge teeth are present, nor is even a ligament formed, 

 an organ that is present in all other Lamellibranchs, except the 

 members of this family and the next one to be considered ; besides 

 this a new element is found, namely accessory shell pieces. The 

 enormously developed siphon, is four or five times the size of the 

 rest of the body. The mantle edges are firmly united except at the 

 oral pole where the boring foot protrudes, and at the openings of 

 the siphon. The true shells as well as the accessory pieces are 

 movable, that is, not united with the calcareous secretion of the 

 mantle. 



In GastrocJiaena the shells are very small, but still movable, the 

 animal being enclosed in a calcarfous shell, the secretion of the 

 siphon. In Clavagella, a similar form, one shell is welded to the 

 siphon shell, the right one only being free, and in the extreme form 

 of Aspergillum, both shells are immovably fixed in the shelly tube 

 that encloses the animal. 



The fresh-water forms Cyclas, Cyprina etc., are probably related 

 to Cardiimi and have received their new forms by moving into fresh 

 water. 



In summing up. Dr. Sharp showed two branches in the Lamelli- 

 branchiata, one going off from a form related to Area the other 

 toward Ostrea, the fulcrum moving from a position between tlie two 

 equally large adductors, toward the oral pole of the body. This 

 brought the anterior adductor in a line with the fulcrum and poste- 

 rior adductor, where, being of no use, it disappeared. 



In the other direction, development is in the antero-posterior 

 direction, the shell, however, not taking part in the growth until a 

 form is reached where the shell is exceedingly small and the animal 

 protected by a supplementary deposit of carbonate of lime. 



March 13. 

 Mr. Charles Roberts, in the chair. 

 Seven persons present. 



March 20. 



The President, Dr. Joseph Leidy, in the chair. 



Habit of Oirolana concharum. — Prof. Leidy said that he yesterday 

 went to Atlantic City, in the expectation of finding interesting speci- 

 mens cast ashore in the recent storm; biit there proved to be nothing. 



