1889.] Zoology. 1097 
the order Anomalodesmacea containing the sub-orders Solenomyacea, 
Anatinacea, Myacea, Eusiphonacea, and Adesmacea. The prionodont 
type has the hinge with teeth transverse to the long axis of the shell 
and is characteristic of the order Prionodesmacea with the sub-orders 
Nuculacea, Arcacea, Naiadacea, Trigonacea, Mytilacea, Pectin acea, 
Anomiacea, Ostracea. A pure orthodont type of hinge hardly exists. 
In this the hinge should be longitudinally plicate. Usually however it 
is combined with the prionodont type. This mixed condition finds 
exemplification in the order Teleodesmacea embracing the sub-orders 
Tellinacea, Solenacea, Mactracea, Carditacea, Cardiacea, Chamacea 
(? Rudistes), Trinacreacea, (?) Leptonacea, Lucinacea, (?) Isocardiacea, 
Veneracea. A classification of this sort is convenient, but it seems to 
the present writer no more satisfactory than its predecessors, based as it 
is on the characters of a single structure. Adequate reasons for the 
substitution of the Goldfussian name Pelecypoda for the more familiar 
Lamellibranchiata and Acephala are not apparent, although Dr. Dall is 
in good company in this respect. 
A Remarkable Crustacean. — Dr. G. H. Flower describes' under 
the name Petrarca bathyactidis, a parasitic crustacean found in the 
abyssal anthozoan, Bathyactis symmetrica. The animal is nearly 
spherical, 1.5 to 1.8 mm in diameter, and has much of the general 
structure of a Lepas without the peduncle. The penis is bent foward . 
under the thorax, the legs are reduced, and the mantle is with- 
out calcareous plates. The appendages consist of a pair of preoral 
antennse, a pair of weak mandibles lying in an oral cone, and six pairs 
of postoral (thoracic) appendages which are not biramose. The ali- 
mentary canal consists of three median caecal portions (there being no 
anus) and the paired hepatopancreas. The nervous system is ex- 
tremely reduced and is not divided into ganglia. The annual is her- 
maphroditic. No sense organs were recognised. Petrarca is regarded 
as closely allied to Laura and Synagoga, and all are placed in the group 
Ascothoracida. This group is regarded in many respects as interme- 
diate between the Ostracoda and the Cirripedia, Petrarca leaving the 
main stem later than i 
Anatomy of Polyxenus.— Heathcote has studied* some points 
in the structure of this interesting Myriapod. The account of the 
external genitalia given by Latzel is confirmed. Two Malpighian 
tubes occur bound to the rectum by a common membrane. The nerve 
