ANIMALS. 141 



former with a rudimentary apophysary system in the form of isolated plates, and the 

 latter apparently without any, I have made free to make a trifling addition to Mr. 

 Gray's diagnosis, so as to qualify it for the reception of what appear to be a few 

 exceptional cases. 



I purpose, in the next place, adverting to the families herein included in the present 

 order, briefly noticing those, and their constituent genera, which are not Permian for 

 the sake of comparing them with the Permian groups. 



Family Strigocephalid^, King. 



This group is typified with the genus Strigocephalus, and diS'ers from its equivalents 

 chiefly in certain of its cardinal characters, — notably its foraminated deltidium, which 

 resembles that of Orthisina ; and in its enormously developed ventral median plate, 

 cardinal boss or muscular fulcrum, and (sub-marginal, anneliform) loop.^ It seems 

 to be confined to the Devonian system. 



Family Rhynchorid^, King. 



This group I propose typifying with the genus BhyncJwra. It diS'ers from 

 TerehratulidcB in generally possessing an area, and a sub-apical foramen ; and perhaps 

 in its normal members being without a loop. The absence of the last character is to 

 a certain extent supported by a figure of BhyncJtora spathulata, Wahlenb. in the 

 ' Lethea Svecica' (PL XXII, fig. 9 h), and by another in the ' Lethsea Geognostica' 

 (PI. XXX, fig. 5 d) of the interior of Belthyridaa jjectiniformis {Tereh. id., J. Sow.), 

 both of which appear to be as much divested of an apophysary system as an Orthis, 

 or any other Sarcicobrachial palliobranch. The same negative character appears to be 

 confirmed by the interior of a Bhynchora costata, Wahlenberg, with which, including 

 several other Swedish fossils, I have been kindly supplied by M. Clason, of Fuhrdal, 

 in Delacarlia. 



Besides the typical genus (typified with Bhynchora costata, Wahl.), the present 

 family embraces BeWiyridisa,'^ M'Coy (the type of which appears to be the Terehratula 

 pectiniformis), and the one next to be noticed. 



1 For a description of the internal structure of Strigocephalus, vide ante, pp. 70-72. 



2 Kcenig founded the genus Trigonosemus on a shell named Trigonosemus elegans (Icon. Foss., Sect., 

 p. 3, pi. vi, fig. 73). Taking into consideration the external characters of Terehratula lyra, Sow., which 

 is also included in the genus, Trigonosemus appears to be synonynaous with Delthyridma ; but as I am totally 

 unacquainted with the type just named, it is impossible for me to give a positive opinion on the subject. 

 It would be well if the original specimen of Trigonosemus elegans were fully described. 



