TUNICATA BTtYOZOA. 



153 



No. 755. ProdTlCtUS gigailteilS, Martin. 



An unusually large specimen from the Carboniferous limestone of Derbyshire, 

 England, and now in the Ward Museum of the University of Rochester. 



Size, 6x4. Price, $0.90. 



No. 756. Discina ampla. 



This representative of the Discinidae is from the Oriskany sandstone, Alba- 

 ny Co., N. Y, ■ Pl>ice > $ - 35 - 



No. 757. Trematospira multistriata, Hall. 



This Brachiopod has the internal spires of Spirifer and the beak of Atrypa. 

 From the Lower Helderberg (Upper Silurian), Albany Co., N. Y. Price, $0.15. 



This entire Suite of Brachiopoda, — Nos. 690-757, — includes 65 species and 

 17 genera, represented by 74 specimens. Price, packed, $20.00. 



CLASS VI.— TUNICATA. 



These " cloaked" Molluscs, represented by the Ascidians, are invest- 

 ed in a leathery tunic, answering to the shells of the Bivalves. This 

 covering is unlike anything else in the Animal Kingdom in that it is 

 composed chiefly of vegitative cellulose. The blood is carried backwards 

 and forwards along the same vessels, as was supposed to be the case 

 in the human system before the time of Harvey. " The Tunicates 

 (says Milne Edwards) depart from the Molluscan type in mode of cir- 

 culation, in the metamorphosis which the fry undergo, and above all in 

 the singular power which most of them possess of multiplying by gem- 

 mation." The Tunicates exist in all seas from low-water to a consider- 

 able depth. Owing to the absence of calcified parts, they have not been 

 found fossil. 



CLASS VII.— BRYOZOA. 



These " moss animals," the Polyzoa of Thompson (including, 

 according to Agassiz, the Vorticellse) , constitute the lowest class of the 

 sub-kingdom. In the words of the Cambridge Professor, they are 

 " depauperated Mo.lluscs." Long confounded with Zoophytes, they were 



