TUNICATA. 85 



Order 2. TESTICARDINES. 



The shell is calcareous, with hinge and brachial skeleton. The 

 intestine ends blindly. 



The exclusively fossil families of the Orthidae and Productidee (Productus 

 Sav.), the edge of the shells which have no hinge, form the transition between 

 the two orders. 



Fam. Khynchonellidae. Rhynohonella psittacea Lam., fossil species found in 

 the Silurian. Pentamerus Sow., contains only fossil species from the Silurian 

 and Devonian formations. The fossil Spiriferidce are allied here (Spirifer 

 Sow.). 



Fam. Terebratulidae. Thecidium mediterraneum Biss., Waldheimia King ; 

 T&rebratula mtrea Lam., Mediterranean ; Terebratulina oaput serpentis L., 

 North Sea ; Argiope Dp. 



CHAPTER III. 

 TUNICATA* 



Bilateral, saccidar, or barrel-shaped animals ; the respiratory cavity 

 with two wide openings, between which is placed a simple nerve 

 ganglion. Bfeart and branchiae are present. 



The Tunicata owe their name to the presence of a gelatinous or 

 cartilaginous envelope or mantle (the tunica externa or testa), which 

 completely surrounds the body. The body is saccular (Ascidians) 

 or barrel-shaped (Salpce). In all cases there is at the anterior end 

 a wide opening (figs. 558, 559, 0), which can be closed by means of 

 muscles, and often also by valves. Through this opening water and 

 nutrient matters pass into the pharyngeal cavity, which also serves 

 as a respiratory organ. At some distance (Ascidians) from this first 

 opening, or at the opposite end of the body (Salpm), there is a second 

 opening (figs. 558, 559 A), which can also be closed; this serves as 

 the exhalent opening of the cloacal cavity (.27), which communicates 

 with the pharyngeal cavity. 



* J. C. Savigny, " Me'moires sur les animaux sans vertebres, II." Paris, 

 1815. 



Chamisso, " De animalibus quibusdam e classe Vermium." Berlin, 1819. 



Milne Edwards, " Observations sur les Ascidies compose'es de cotes de la 

 Manche." Mem. Acad. Se. Paris, 1839. 



A. Kowalevski, " Weitere Studien iiber die Entwickelung der einfachen 

 Ascidien." Arch.fiir mikr. Anatomic, Taf. VI., 1870. 



