302 MOLLUSCOIDEA SUB-KINGDOM V 
becomes the pedicle, and may in this stage serve to attach the larvae to foreign objects, 
or the pedicle may remain undeveloped for a time. A rudimentary digestive tract is 
present, and also four pairs of muscles, which later become the adductor, diductor, and 
ventral pedicle muscles. 
In the Phylembryo the embryonic shell, or protegulum, is completed ; the tentacular 
lobes of the lophophore, or brachia, appear; the four bundles of setae are dehisced ; 
obsolescence of the eyes occurs, as well as the agree- 
ment of the muscular system with that in adult forms. 
The protegulum has been observed by Beecher in 
many genera, representing nearly all the leading 
families of the class, and therefore it may be inferred 
that the protegulum is common to all Brachiopods. 
It is semi-circular or semi-elliptical in outline, with a 
A 

Fia. 503. 
Cistella Neapolitana, Schacchi. 
A, Phylembryo; Brachiopod show- 
ing shell (protegulum), beginning 
of tentacles of lophophore (J), ob- 
solescence of eye-spots, and forma- 
tion of oesophagus ; t, Hinge-teeth ; 
vp, Ventral pedicle muscles. B, 

. AYES 
Fic, 502. Nepionic Brachiopod, showing 
Cistella Neapolitana, Schacchi. A, Neoembryo; completed cepha- distinct tentacles of lophophore, 
lula stage. B, Typembryo; transformed larva resulting from folding mouth and stomach, and trans- 
upwards of mantle lobes over cephalic segment; ad, Muscles from formation of muscles from typem- 
bundles of setae to sides of body cavity; di, Muscles from dorsal to bryo; ad, Adductors ; di, Divari- 
ventral sides of body ; vp, Muscles from ventral side of body to caudal cators ; vp, Ventral pedicle muscles 
segment or pedicle (after Kovaleyski, from Beecher). (after Kovalevski, from Beecher). 
straight or arcuate hinge-line, and no cardinal area. The prototype preserving 
throughout its development the main features of the protegulum, and showing no 
separate or distinct stages of growth, is 
represented by the genus Paterina (Fig. 
505). 
So far as observed, the proteguluin, 
or Paterina stage, in the Atremata and 
Telotremata is followed by the Obolella 
stage of nearly circular outline. After 
Thecidia (Lacazella) Mediterranea, Risso. Recent. this stage, specific characters appear, and 
a Dorso - ventral longitudinal section of cephalula ; in the open delthyrium of the Telotremata 
1, Head ; d, Dorsal mantle lobe ; v, Ventral mantle lobe ; 
ds, Beginning of dorsal valve; del, Shell plate forming there are usually developed the first rudi- 
Tongitudinal section of typembryos os, Ventral valve; ments of the deltidial plates. In the 
hl, Hinge-line of dorsal valve. C, Adult specimen seen Protremata, the Paterina stage 1s not 
(Hand Batter Kovalevski after Beroher.) """ followed by the Obolella stage, but the 
wide delthyrium of the protegulum is at 
once affected and modified by the prodeltidium, which develops into the deltidium. 
In the Acrotretacea, belonging to the Neotremata, there is often developed a true 
deltidium, showing the close relationship of the order with the Protremata, and the 
dissimilarity of these two orders to Atremata and Telotremata. In the Discinacea, 
belonging to the Neotremata, the pedicle opening is an open notch in the posterior 

Fic. 504. 
